United States v. Zackary Jackson ( 2019 )


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    DISTRICT OF COLUMBIA COURT OF APPEALS
    No. 16-CO-523
    UNITED STATES, APPELLANT,
    V.
    ZACKARY JACKSON, APPELLEE.
    Appeal from the Superior Court
    of the District of Columbia
    (CF3-2512-15)
    (Hon. Maribeth Raffinan, Trial Judge)
    (Argued October 26, 2016                             Decided August 22, 2019)
    Nicholas P. Coleman, Assistant United States Attorney, with whom
    Channing D. Phillips, United States Attorney at the time the brief was filed, and
    Elizabeth Trosman, Chrisellen R. Kolb, Alicia M. Long, and Anwar Graves,
    Assistant United States Attorneys, were on the brief, for appellant.
    Daniel Gonen, Public Defender Service, with whom Samia Fam and Jaclyn
    Frankfurt, Public Defender Service, were on the brief, for appellee.
    Before BLACKBURNE-RIGSBY, * Chief Judge, GLICKMAN, Associate Judge,
    and WASHINGTON, † Senior Judge.
    *
    Chief Judge Blackburne-Rigsby was an Associate Judge at the time oral
    argument was held on October 26, 2016. Judge Blackburne-Rigsby assumed the
    duties of Chief Judge on March 18, 2017.
    2
    GLICKMAN, Associate Judge: The United States appeals a pretrial order
    suppressing appellee Zackary Jackson’s Global Positioning System (GPS) tracking
    data and derivative evidence in its prosecution of Mr. Jackson for armed robbery.
    The tracking data was collected and maintained by the District of Columbia Court
    Services and Offender Supervision Agency (CSOSA) after it required Mr. Jackson
    to wear a GPS tracking device on his ankle as a sanction for his having violated
    conditions of his probation in an earlier case. CSOSA gave the police access to the
    GPS data, and the data revealed to the police that Mr. Jackson was present at the
    scene of the armed robbery with which he is now charged. The police used the
    data to track Mr. Jackson from the location of the robbery to his home, where they
    arrested him and found tangible evidence linking him to the crime.
    In moving to suppress the GPS data and its fruits, Mr. Jackson argued that
    CSOSA violated his Fourth Amendment rights by placing him on GPS monitoring
    for purposes of law enforcement without judicial authorization and that the police
    violated his Fourth Amendment rights by accessing the GPS tracking data without
    (…continued)
    †
    Senior Judge Pryor, who was assigned to this case originally and at the
    time of oral argument, retired on May 15, 2019. Senior Judge Washington was
    assigned to take his place on the division.
    3
    a search warrant. Addressing only the latter issue, the motions judge concluded
    that the police search infringed Mr. Jackson’s reasonable expectation of privacy in
    his GPS data and, therefore, violated his Fourth Amendment rights.
    We reverse. First, as a threshold matter, we hold that CSOSA’s imposition
    of GPS monitoring on Mr. Jackson without judicial authorization was a
    constitutional “special needs” search; it was constitutional because his reasonable
    expectation of privacy as a convicted offender on probation was diminished and
    was outweighed by the strong governmental interests in effective probation
    supervision to deter and detect further criminal activity on his part and encourage
    his rehabilitation. We reject, as unsupported by the record, Mr. Jackson’s claim
    that CSOSA placed him on GPS monitoring as a subterfuge to enable the police to
    avoid having to comply with the warrant and probable cause requirements of the
    Fourth Amendment. Second, we conclude that Mr. Jackson had no objectively
    reasonable expectation that CSOSA would withhold the GPS tracking data from
    the police. The limited police examination of that data—which focused solely on
    determining whether any monitored CSOSA supervisee was present during the
    armed robbery (and if so, where that supervisee went immediately afterwards)—
    therefore did not violate Mr. Jackson’s Fourth Amendment rights.
    4
    I.
    A. Mr. Jackson’s Placement on GPS Monitoring
    On December 13, 2013, Mr. Jackson pleaded guilty in Superior Court to one
    count of attempted robbery. Mr. Jackson had been charged with armed robbery.
    In tendering his guilty plea to the lesser offense, he admitted that he and two
    accomplices put on masks inside the Benning Road Metro station and robbed the
    victim of his cell phone by threatening him with a BB pistol.
    Three months later, the judge sentenced Mr. Jackson to twelve months’
    incarceration, with all but four months suspended in favor of one year of probation
    under the supervision of CSOSA. The court-imposed conditions of his probation
    included requirements that Mr. Jackson (1) “[o]bey all laws, ordinances, and
    regulations”; (2) permit his Community Supervision Officer [CSO] to visit his
    place of residence; (3) report to all scheduled appointments with his CSO; (4)
    notify his CSO within one business day of any arrest or questioning by a law
    enforcement officer; (5) submit to drug testing at the discretion of CSOSA; (6)
    participate in and complete CSOSA programs as directed; and (7) “[i]n the event of
    illicit drug use or other violation of conditions of probation, participate as directed
    5
    by [his] CSO in a program of graduated sanctions that may include periods of
    residential placement or services.”
    Mr. Jackson’s period of probation began in July 2014. It did not go well.
    Mr. Jackson failed to report for scheduled appointments with his CSO on five
    occasions, in August, December, and January; he did not pursue gainful
    employment as required by CSOSA programming; and on December 23, 2014, Mr.
    Jackson was re-arrested in Virginia.1
    Thereafter, in January 2015, a detective with the Metropolitan Police
    Department (MPD) contacted CSOSA to request that Mr. Jackson be placed on
    GPS monitoring, one of the options in CSOSA’s program of graduated sanctions
    for non-compliant behavior. As stated in CSOSA’s internal emails, the detective
    made this request because the police believed Mr. Jackson and another named
    individual “may” have been committing robberies and burglaries together at a
    1
    According to CSOSA’s running record of Mr. Jackson’s supervision, he
    was released following his new arrest and was due back in court the following
    month. In the hearing below on the evidence suppression motion, counsel for the
    United States represented that Mr. Jackson was arrested in Virginia for “a felony
    pickpocket.” The record on appeal does not appear to provide any additional
    information about the nature of the charge in Virginia or the outcome of the
    proceedings there.
    6
    particular Metro station in the District and elsewhere. The police request triggered
    a review by CSOSA of Mr. Jackson’s compliance with his terms of probation to
    determine whether he met the agency’s criteria for GPS monitoring. Citing Mr.
    Jackson’s re-arrest, lack of employment, and failure to look for work and
    participate in CSOSA programming, the agency decided he should be placed on
    GPS monitoring “immediately.” 2
    Mr. Jackson’s CSO met with him on January 28, 2015. She questioned him
    about his missed appointments and his involvement in criminal activity (which he
    denied), and she informed him that he would be placed on GPS monitoring.
    According to her record of the meeting, Mr. Jackson was “visibly upset” by that
    decision and “stated he wouldn’t be able to do anything.” The CSO emphasized
    2
    CSOSA’s published Policy Statement 4008, “Global Positioning System
    (GPS) Tracking of Offenders,” effective May 7, 2009, https://www.csosa.gov/wp-
    content/uploads/bsk-pdf-manager/2018/03/4008_gps_tracking_050709.pdf          (last
    visited June 13, 2019), sets forth the procedures CSOSA follows in connection
    with the imposition of GPS tracking of offenders. The Policy Statement provides
    that an offender under supervision may be referred for placement on GPS as a
    sanction if, among other things, the offender is re-arrested and released into the
    community pending further judicial action, or if the offender is unemployed, at a
    maximum or intensive level of supervision, and not actively searching for
    employment or in school or a training program.
    7
    that although Mr. Jackson would not have a curfew, “he must be aware that
    [CSOSA] will be tracking his whereabouts for at least 30 days.”3
    The next day, Mr. Jackson reported to CSOSA for the GPS device – a small
    bracelet transmitter with a strap – to be fitted and attached to his ankle. He signed
    a “CSOSA Global Positioning System (GPS) Contract,” in which he acknowledged
    his understanding that “all GPS activities will be monitored by CSOSA’s (24/7)
    Monitoring Center,” and that “all movement will be tracked and stored as an
    official record.” The contract required Mr. Jackson to wear the GPS device at all
    times and not to tamper with it for any reason. It also required him to charge the
    device twice a day, an hour in the morning and an hour in the evening, and not to
    sleep while the device was charging. The contract stated that the device was
    waterproof and did not prevent him from taking showers, but that he should not
    submerge the device in water (meaning he could not bathe or swim while wearing
    it).
    3
    CSOSA’s Policy Statement on GPS tracking of supervised offenders,
    supra, footnote 2, provides that when GPS tracking is employed as a sanction for
    non-compliant behavior, it may be implemented for up to thirty days and, when
    aggravating circumstances exist, extended for up to a total of ninety days.
    8
    B. An Armed Robbery and Its Investigation
    Early on the morning of February 19, 2015 (less than three weeks after Mr.
    Jackson began wearing the GPS device), police received a report of an armed
    robbery in the 4400 block of C Street in Southeast Washington, D.C. As the
    victims, Mr. Parker and Ms. Pleasant, described the incident, they were walking
    home together and, after turning from Texas Avenue onto C Street, they passed by
    an alley on their left. In the alley, they noticed a newer model black SUV that
    pulled out and drove toward the intersection of Texas Avenue and C Street. Mr.
    Parker looked back and saw the SUV pause at the traffic light there. Ms. Pleasant
    asked him what time it was, and Mr. Parker checked his cell phone and told her it
    was 1:36 a.m.
    As he put the cell phone back in his pocket, Mr. Parker looked back again
    and saw the SUV speeding toward him and Ms. Pleasant in reverse. The SUV
    stopped right in front of them. Two men got out of the back seats. One displayed
    a small, black handgun and took Mr. Parker’s wallet. The other man took Ms.
    Pleasant’s purse. The two men then returned to the SUV, which drove off toward
    Texas Avenue. The two victims got home and called the police.
    9
    Detective Thomas O’Donnell of the MPD interviewed the complainants
    shortly after they reported the robbery. Although they provided detailed physical
    descriptions of their assailants, the robbers’ identities were unknown and there
    were no suspects or other witnesses. Detective O’Donnell decided to run a check
    to determine whether any supervisees under GPS monitoring by CSOSA were at
    the crime scene at the time of the offense. He had access to the computerized GPS
    tracking data pursuant to a Memorandum of Understanding in which CSOSA
    agreed to share it with the MPD and allowed the police to query the database
    directly. 4 The monitoring system tracks and records the movements of the GPS
    devices in one-minute increments, twenty-four hours a day, seven days a week.
    Detective O’Donnell entered the coordinates of the crime scene into the database
    to determine whether any monitored supervisees were in the area between 1:20
    a.m. to 1:45 a.m.
    His GPS check produced two hits. It revealed that Mr. Jackson and another
    CSOSA supervisee were in the alley where the victims saw the SUV just before
    the robbery occurred. From the alley, their movements conformed to the victims’
    observations of their attackers: the GPS data showed that Mr. Jackson and the
    4
    We describe this sharing arrangement further in Part II.B of this opinion.
    10
    second person moved toward the intersection of Texas Avenue and C Street, then
    went back into the 4400 block of C Street, and then went back to Texas Avenue.
    The GPS data also allowed the police to track the two suspects’ subsequent
    movements as they briefly separated and then reunited in the rear parking lot of
    4410 E Street, Southeast. The data showed that Mr. Jackson then went into an
    apartment at 4410 E Street and that the other suspect went to a location a block
    away.
    The police immediately went to the two destinations. They arrived at Mr.
    Jackson’s apartment building between 2:00 and 3:00 a.m. Mr. Jackson’s GPS
    device continued to show him as being there. In the rear parking lot, the officers
    saw a black, newer model SUV.           Mr. Parker, who accompanied Detective
    O’Donnell, identified the SUV as the one the robbers used. 5 On the ground near
    the stairs leading to the building entrance, the police found a bank card in Mr.
    Parker’s name.
    The police proceeded to Mr. Jackson’s apartment to arrest him and secure
    the location while they applied for a warrant to search it. In the apartment, they
    5
    WALES and NCIC checks indicated that the SUV had been stolen.
    11
    found Mr. Jackson with three other people. After obtaining the search warrant, the
    police recovered the keys to the SUV and some items that may have been in Ms.
    Pleasant’s purse.6
    Mr. Jackson was arrested. He subsequently was charged by indictment with
    two counts of armed robbery, first-degree theft (of the SUV), and unauthorized use
    of a vehicle (the SUV) to facilitate a crime of violence.
    C. The Trial Court’s Suppression of the Evidence
    Following his arraignment, Mr. Jackson moved to suppress the electronic
    and tangible evidence linking him to the robberies. Among his claims, he argued
    that his Fourth Amendment rights were violated by CSOSA’s imposition of GPS
    monitoring at the behest of the police and by the subsequent warrantless police
    search of the GPS tracking data. After a hearing, and on largely undisputed facts,
    the motions judge granted the motion to suppress on the latter ground, that the
    police search of the GPS data was unconstitutional. The judge did not address the
    constitutionality of CSOSA’s GPS monitoring of Mr. Jackson.
    6
    The police also searched the second suspect’s residence. They reportedly
    found him in a downstairs bedroom, lying on top of a cell phone that matched the
    description of the phone in Ms. Pleasant’s stolen purse.
    12
    The judge based her ruling on her conclusion that Mr. Jackson reasonably
    expected that the police would not have access to his GPS tracking data. In
    reaching that conclusion, the judge acknowledged that Mr. Jackson was on
    probation and that, “[g]iven the language of the GPS Contract, it would be
    unreasonable for Jackson to expect privacy in his GPS location information as to
    CSOSA.” (Emphasis added.) However, the judge noted, the conditions of Mr.
    Jackson’s probation and his GPS Contract did not inform him, “clear[ly] and
    unambiguous[ly],” that the location data would be shared with or accessible to the
    police. Absent such notification, the judge stated, Mr. Jackson “could not have
    reasonably foreseen that the MPD would have unfettered, unilateral access to his
    location information for developing suspects and finding witnesses in criminal
    cases.” Because the police lacked “any level of individualized suspicion” linking
    Mr. Jackson to the robberies before they queried the GPS database, the judge
    concluded that Mr. Jackson’s undiminished expectation of privacy vis-à-vis the
    police outweighed “the MPD’s general interest in criminal investigation.”
    Accordingly, the judge held, the police search of Mr. Jackson’s GPS location data
    was “unreasonable under the Fourth Amendment.”
    13
    II.
    Two distinct Fourth Amendment issues are presented in this appeal. Given
    the undisputed factual record before us, each turns on legal questions that we
    decide de novo.     The first is whether CSOSA violated Mr. Jackson’s Fourth
    Amendment rights by placing him on GPS monitoring without judicial approval.
    This issue turns, as we shall explain, on whether the monitoring was justified as a
    reasonable intrusion on Mr. Jackson’s privacy to meet the “special needs” of
    probation supervision. We address this legal issue, even though the motions judge
    granted suppression for other reasons, because it was litigated in the proceedings
    below, Mr. Jackson continues to urge it on appeal as an alternative ground for
    affirmance, and the United States has had a full and fair opportunity to rebut the
    claim. 7 Moreover, our resolution of the second Fourth Amendment issue before us
    depends on our answer to the first issue.
    The second issue is whether the police conducted an unconstitutional search
    when, without having a search warrant or individualized suspicion, they queried
    CSOSA’s GPS database and acquired the information it contained about Mr.
    7
    See Ibn-Tamas v. United States, 
    407 A.2d 626
    , 635-36 (D.C. 1979).
    14
    Jackson’s location and movements at the time and in the immediate vicinity of the
    robbery. Assuming the lawfulness of CSOSA’s acquisition of that information in
    the first place, this issue turns in our view on whether CSOSA violated Mr.
    Jackson’s reasonable expectation of privacy by allowing the police to access its
    GPS database for the limited use the police made of it.
    We address these two issues in turn.8
    8
    In the proceedings below, the United States argued that CSOSA’s
    imposition of GPS monitoring did not violate Mr. Jackson’s Fourth Amendment
    rights because he consented to it when he agreed to the GPS contract. See
    generally Schneckloth v. Bustamonte, 
    412 U.S. 218
    (1973). Mr. Jackson disputed
    that claim, arguing that his mere acquiescence to the monitoring did not amount to
    a valid waiver of his Fourth Amendment rights. The motions judge did not address
    this issue of consent in her decision, and while the United States does not concede
    the issue, it has not pressed the consent argument on appeal. We do not find it
    necessary to reach the question; to quote the Second Circuit’s observation in a
    similar case, “[t]he issue here … is not so much whether [Mr. Jackson] gave
    consent as it is whether he had a reasonable and legitimate expectation of privacy.”
    United States v. Lambus, 
    897 F.3d 368
    , 410 (2d Cir. 2018); see also United States
    v. Knights, 
    534 U.S. 112
    , 118 (2001) (refraining from deciding whether
    probationer’s acceptance of a search condition “constituted consent in the
    Schneckloth sense of a complete waiver of his Fourth Amendment rights,” because
    the Court could conclude that the search “was reasonable under our general Fourth
    Amendment approach of ‘examining the totality of the circumstances,’ . . . with the
    probation search condition being a salient circumstance” (internal citation
    omitted)).
    15
    A. CSOSA Did Not Violate Mr. Jackson’s Fourth Amendment Rights
    by Placing Him on GPS Monitoring and Tracking His Movements.
    1. The Special Needs of Probation Supervision Recognized in
    Griffin v. Wisconsin
    It is common ground that when the government “attaches a device to a
    person’s body, without consent, for the purpose of tracking that individual’s
    movements,” it conducts a search subject to the Constitution’s requirements. 9 The
    government’s use of the device to monitor the person’s movements also constitutes
    a search for Fourth Amendment purposes. 10
    The Fourth Amendment to the Constitution protects the right of the people
    to be secure against searches and seizures that are “unreasonable.”11 Thus, as
    “[t]he touchstone of the Fourth Amendment is reasonableness,” 12 the central
    question before us is the reasonableness vel non of CSOSA’s GPS monitoring of
    Mr. Jackson.       Resolution of this question “depends on the totality of the
    circumstances, including the nature and purpose of the search and the extent to
    9
    Grady v. North Carolina, 
    135 S. Ct. 1368
    , 1370 (2015).
    10
    See United States v. Jones, 
    565 U.S. 400
    , 404 (2012).
    11
    U.S. Const. amend. IV.
    12
    
    Knights, 534 U.S. at 118
    .
    16
    which the search intrudes upon reasonable privacy expectations.” 13 We determine
    whether a search is reasonable “by assessing, on the one hand, the degree to which
    it intrudes upon an individual’s [reasonable expectation of] privacy and, on the
    other, the degree to which it is needed for the promotion of legitimate
    governmental interests.”14     The Supreme Court has characterized this as a
    balancing test.15
    “Where a search is undertaken by law enforcement officials to discover
    evidence of criminal wrongdoing, . . . reasonableness generally requires the
    obtaining of a judicial warrant” upon the showing of probable cause required by
    the Fourth Amendment’s Warrant Clause.16 But the Court has explained that:
    13
    
    Grady, 135 S. Ct. at 1371
    .
    14
    
    Knights, 534 U.S. at 118
    -19 (quoting Wyoming v. Houghton, 
    526 U.S. 295
    , 300 (1999)).
    15
    See, e.g., Vernonia Sch. Dist. 47J v. Acton, 
    515 U.S. 646
    , 652-53 (1995)
    (“At least in a case such as this, where there was no clear practice, either approving
    or disapproving the type of search at issue, at the time the constitutional provision
    was enacted, whether a particular search meets the reasonableness standard ‘“is
    judged by balancing its intrusion on the individual’s Fourth Amendment interests
    against its promotion of legitimate governmental interests.’” (quoting Skinner v.
    Ry. Labor Execs.’ Ass’n, 
    489 U.S. 602
    , 619 (1989))).
    16
    
    Acton, 515 U.S. at 653
    .
    17
    [A] warrant is not required to establish the
    reasonableness of all government searches; and when a
    warrant is not required (and the Warrant Clause therefore
    not applicable), probable cause is not invariably required
    either. A search unsupported by probable cause can be
    constitutional . . . “when special needs, beyond the
    normal need for law enforcement, make the warrant and
    probable-cause requirement impracticable.”[17]
    Nor do searches motivated by “special needs, beyond the normal need for law
    enforcement” necessarily require a degree of “individualized suspicion of
    wrongdoing” in the absence of probable cause; “the Fourth Amendment imposes
    no irreducible requirement of such suspicion.” 18
    In Griffin v. Wisconsin, the Supreme Court considered whether the operation
    of a probation system presents “special needs” beyond the normal need for law
    enforcement that may justify exempting supervisory searches of probationers from
    17
    
    Id. (quoting Griffin
    v. Wisconsin, 
    483 U.S. 868
    , 873 (1987)).
    18
    
    Id. (quoting United
    States v. Martinez-Fuerte, 
    428 U.S. 543
    , 560-61
    (1976)). The Court has upheld suspicionless searches and seizures under “special
    needs” or similar rationales in a variety of situations – for instance, in 
    Acton, 515 U.S. at 653
    -65 (upholding random urinalysis drug testing of students in school
    athletics programs; 
    Skinner, 489 U.S. at 633-34
    (drug testing of railroad personnel
    involved in train accidents); Nat’l Treasury Emps. Union v. Von Raab, 
    489 U.S. 656
    , 666, 676 (1989) (drug tests for U.S. Customs Service employees seeking
    transfers or promotions); New York v. Burger, 
    482 U.S. 691
    , 702-04 (1987)
    (warrantless administrative inspections of the premises of “closely regulated”
    businesses).
    18
    the requirements the Fourth Amendment imposes on “normal” law enforcement
    searches. The question arises, even though both types of searches aim to discover
    evidence of criminal activity, because supervisory searches of probationers are
    unlike “normal” law enforcement searches in that they are conducted as part of the
    distinctive probation mission to reform convicted offenders and deter them from
    committing new crimes. The Court was persuaded in Griffin of the significance of
    this contextual difference, and it applied the “special needs” rationale to uphold a
    warrantless search of a probationer’s home under circumstances parallel, in
    important respects, to those in this case.
    The facts of Griffin were as follows. Under Wisconsin law, probationers
    were subject to the conditions of probation set by the court at sentencing and to the
    regulations of the probation department.          One such regulation allowed any
    probation officer to search any probationer’s home, without a warrant or other
    prior judicial approval, so long as there were “reasonable grounds” to believe
    19
    contraband was present in the home. 19 This home-search authorization was not
    one of the court-imposed conditions of Griffin’s probation. 20
    While Griffin was on probation, the probation office received information
    from a police detective that “there were or might be guns” in Griffin’s apartment.21
    Two probation officers, accompanied by three police officers, went there to find
    out. Relying on the home-search regulation, they did not apply for a search
    warrant. When Griffin opened the door, one of the probation officers “informed
    him that they were going to search his home.” 22 They found and seized a handgun.
    Griffin was prosecuted for felony possession of a firearm. He moved to suppress
    the handgun, arguing that the probation officers’ search of his home without a
    19
    
    Griffin, 483 U.S. at 871
    ; see also 
    Knights, 534 U.S. at 117
    (“The
    regulation applied to all Wisconsin probationers, with no need for a judge to make
    an individualized determination that the probationer’s conviction justified the need
    for warrantless searches.”).
    20
    In fact, the regulation was not promulgated until a year after Griffin was
    sentenced and placed on probation. See 
    Knights, 534 U.S. at 117
    & 117 n.2 (citing
    
    Griffin, 483 U.S. at 870
    , 871).
    21
    
    Griffin, 483 U.S. at 871
    . The Court considered it “most unlikely” that
    this “unauthenticated tip of a police officer – bearing, as far as the record shows,
    no indication whether its basis was firsthand knowledge or, if not, whether the
    firsthand source was reliable, and merely stating that Griffin ‘had or might have’
    guns in his residence, not that he certainly had them – would meet the ordinary
    requirement of probable cause.” 
    Id. at 878.
          22
    
    Id. 20 warrant
    violated the Fourth Amendment. The court denied the motion and Griffin
    was convicted.
    The Supreme Court held that “[t]he search of Griffin’s home satisfied the
    demands of the Fourth Amendment because it was carried out pursuant to a
    regulation    that   itself   satisfies   the    Fourth   Amendment’s   reasonableness
    requirement” under the “well-established” exception to the warrant requirement for
    “special needs” searches.23 The Court explained its holding as follows. First, it
    perceived it to be “always true of probationers . . . that they do not enjoy ‘the
    absolute liberty to which every citizen is entitled, but only . . . conditional liberty
    properly dependent on observance of special [probation] restrictions’” –
    restrictions “meant to assure that the probation serves as a period of genuine
    rehabilitation and that the community is not harmed by the probationer’s being at
    large.”24 “These same goals,” the Court stated, “require and justify the exercise of
    supervision to assure that the restrictions are in fact observed.” 25 Moreover, the
    Court noted, “[r]ecent research suggests that more intensive supervision can reduce
    23
    
    Id. at 873.
          24
    
    Id. at 874-75
    (quoting Morrissey v. Brewer, 
    408 U.S. 471
    , 480 (1972)).
    25
    
    Id. at 875.
                                                21
    recidivism, . . . and the importance of supervision has grown as probation has
    become an increasingly common sentence for those convicted of serious crimes.”26
    In light of these considerations, the Court concluded that probation supervision “is
    a ‘special need’ of the State permitting a degree of impingement upon privacy that
    would not be constitutional if applied to the public at large.” 27
    Second, the Court found multiple reasons to conclude that the special needs
    of probation supervision make the usual warrant and probable-cause requirements
    of the Fourth Amendment impracticable. It stated:
    A warrant requirement would interfere to an appreciable
    degree with the probation system, setting up a magistrate
    rather than the probation officer as the judge of how
    close a supervision the probationer requires. Moreover,
    the delay inherent in obtaining a warrant would make it
    more difficult for probation officials to respond quickly
    to evidence of misconduct, and would reduce the
    deterrent effect that the possibility of expeditious
    searches would otherwise create. . . . And on the other
    side of the equation—the effect of dispensing with a
    warrant upon the probationer: Although a probation
    officer is not an impartial magistrate, neither is he the
    police officer who normally conducts searches against
    26
    
    Id. 27 Id.;
    see also Ferguson v. City of Charleston, 
    532 U.S. 67
    , 79 n.15 (2001)
    (“Griffin is properly read as limited by the fact that probationers have a lesser
    expectation of privacy than the public at large.”).
    22
    the ordinary citizen. He is an employee of the [state
    probation department] who, while assuredly charged with
    protecting the public interest, is also supposed to have in
    mind the welfare of the probationer . . . . In such a
    setting, we think it reasonable to dispense with the
    warrant requirement.[28]
    The Court also concluded that probation supervision would be “unduly disrupted”
    by a requirement that there be probable cause to search the probationer’s home,
    among other reasons because (1) such a requirement “would reduce the deterrent
    effect of the supervisory arrangement;” (2) “the probation agency must be able to
    act based upon a lesser degree of certainty than the Fourth Amendment would
    otherwise require in order to intervene before a probationer does damage to
    himself or society;” and (3) “it is the very assumption of the institution of
    probation that the probationer is in need of rehabilitation and is more likely than
    the ordinary citizen to violate the law.” 29
    In sum, under the “special needs” analysis of Griffin, the Fourth Amendment
    permits probation supervision to intrude significantly on probationers’ privacy
    without judicial approval or probable cause in order to determine whether they are
    28
    
    Griffin, 483 U.S. at 876-77
    .
    29
    
    Id. at 878-80;
    see also 
    Knights, 534 U.S. at 120
    (“The recidivism rate of
    probationers is significantly higher than the general crime rate.”).
    23
    abiding by the law and the conditions of their probation, because probationers’
    reasonable privacy expectations are diminished and are outweighed by the
    heightened governmental interests in deterring them from re-offending and
    promoting their rehabilitation.30
    2. CSOSA’s Special Need to Use GPS Monitoring as an
    Administrative Sanction for High-Risk Supervisees
    Griffin’s “special needs” analysis applies to CSOSA’s installation of a GPS
    device on Mr. Jackson’s ankle to monitor his movements.          CSOSA is the
    counterpart in the District to the state probation department in Griffin. It is a
    federal agency charged by law with providing “supervision, through qualified
    supervision officers, for offenders on probation, parole, and supervised release
    pursuant to the District of Columbia Official Code.”31
    30
    See also Samson v. California, 
    547 U.S. 843
    , 853 (2006) (“[A] State’s
    interests in reducing recidivism and thereby promoting reintegration and positive
    citizenship among probationers and parolees warrant privacy intrusions that would
    not otherwise be tolerated under the Fourth Amendment.” (citing 
    Griffin, 483 U.S. at 879
    ; 
    Knights, 534 U.S. at 121
    )).
    31
    D.C. Code § 24-133(c)(1) (2012 Repl. & 2018 Cum. Supp.); see Hunt v.
    United States, 
    109 A.3d 620
    , 621 (D.C. 2014).
    24
    To carry out that charge, CSOSA was directed by law to “[d]evelop and
    operate intermediate sanctions” for probationers and other sentenced offenders
    under its supervision. 32 The regulations that CSOSA promulgated to that end are
    the counterpart to the regulation at issue in Griffin. 33 They provide that if a
    Community Supervision Officer (CSO) has “reason to believe” a supervisee is
    “failing to abide by the general or specific conditions of release” or is “engaging in
    criminal activity,” the CSO may address the problem by imposing one or more
    administrative sanctions. 34 We explained the advantages of this option in Hunt as
    follows:
    Sanctions “can be applied short of court or USPC [Parole
    Commission] approval” and enable CSOSA to “provide
    swift, certain, and consistent responses to noncompliant
    behavior.” . . . “Imposing the sanctions quickly and
    consistently may prevent escalation of the offender’s
    non-compliant behavior.” . . . [B]y issuing sanctions,
    CSOSA “introduce[s] an accountability structure into the
    supervision process” without commencing revocation
    proceedings or seeking a hearing for a change in release
    conditions.”[35]
    32
    D.C. Code § 24-133(b)(2)(F).
    33
    See 28 C.F.R. § 810.3 (2003).
    34
    
    Id. at §
    810.3(a).
    35
    
    Hunt, 109 A.3d at 621-22
    (quoting Community Supervision:
    Administrative Sanctions, 68 Fed. Reg. 19738-01 (Apr. 22, 2003)).
    25
    These advantages echo Griffin’s concerns that requiring a warrant would “interfere
    to an appreciable degree with the probation system,” “make it difficult for
    probation officials to respond quickly to evidence of misconduct,” and “reduce the
    deterrent effect that the possibility of expeditious searches would otherwise
    create.” 36
    The administrative sanctions available to the CSO include “[e]lectronic
    monitoring for a specified period of time.” 37 This is the provision under which
    CSOSA utilizes GPS tracking technology. Like the other enumerated sanctions,
    GPS tracking is intrusive, but it directly serves the primary purposes of probation
    supervision. As was proffered to the motions judge in the proceedings below,
    CSOSA’s website publicized and explained its use of GPS monitoring of its
    highest-risk offenders for these purposes as follows:
    CSOSA uses Global Positioning System (GPS) satellite
    monitoring for the highest-risk offenders as part of a
    series of graduated sanctions or as a special condition
    36
    
    Griffin, 483 U.S. at 876
    .
    37
    28 C.F.R. § 810.3(b)(6). Other authorized administrative sanctions listed
    in § 810.3(b) include daily check-ins, increased drug testing and drug abuse
    assessments, community service and increased group activities, placement in a
    residential sanctions facility or residential treatment facility, and restrictions on
    travel.
    26
    imposed by the releasing authority. GPS monitoring is
    used to enforce curfews, establish prohibited/restricted
    areas, and assess and monitor offender movement in the
    community. Depending on the type of GPS technology
    employed with a particular offender, monitoring can be
    performed on an almost real-time basis.
    * * *
    This effective tool allows CSOSA to provide heightened
    supervision of high-risk offenders while allowing such
    offenders to productively rehabilitate in the community.
    On any given day, at least 100 offenders are on GPS
    monitoring. . . . GPS placements typically last between
    14 and 90 days.
    CSOSA staff work daily with the DC Metropolitan
    Police Department (MPD) and other law enforcement
    agencies to match offender GPS coordinates with crime
    locations. Mapping technology allows CSOSA to create
    extremely detailed maps of locations and offender
    movements to aid in suspect apprehension and
    identification of witnesses. CSOSA has trained and
    provided MPD staff with direct access to the GPS system
    for monitoring purposes. MPD’s Intelligence Fusion
    Division, responsible for the collection, analysis, and
    dissemination of information related to violent crimes
    within the District of Columbia, is a regular user of
    CSOSA’s GPS data.[38]
    38
    “Electronic Monitoring, Court Services and Offender Supervision
    Agency      for    the   District    of    Columbia”      (May     5,    2016),
    http://www.csosa.gov/supervision/accountability/monitoring.aspx. This page was
    available on the website when Mr. Jackson was placed on probation and being
    monitored. Although the page has since been removed, similar information is now
    available on CSOSA’s website in its May 7, 2009, Policy Statement 4008; see
    (continued…)
    27
    3. The Reasonableness of CSOSA’s Placement of Mr. Jackson on
    GPS Monitoring
    While probation supervision “is a ‘special need’ . . . permitting a degree of
    impingement upon privacy that would not be constitutional if applied to the public
    at large[,] [t]hat permissible degree is not unlimited.”39 The “impingement” upheld
    in Griffin was a warrantless “special needs” search of a probationer’s home, as
    authorized by the probation department’s regulations, based on reasonable grounds
    to suspect the presence there of contraband. In this case, the “impingement” was
    the warrantless attachment and use of a GPS tracking device, as authorized by
    CSOSA’s regulations, based on reasonable grounds to suspect a probationer might
    be committing new crimes. (Mr. Jackson was not subject to a curfew or a stay-
    away order.) The Fourth Amendment reasonableness inquiry requires us to weigh
    the extent to which such a search violates a probationer’s reasonable privacy
    (…continued)
    footnote 
    2, supra
    . We note that, regardless of the utilization of CSOSA’s GPS
    data by the police, the Policy Statement provides that CSOs are responsible for
    reviewing the GPS tracks of offenders under their supervision on a daily basis, and
    for investigating, reporting, and sanctioning any violations.
    We address the propriety of CSOSA’s sharing of its GPS data with the MPD
    in Part II.B of this opinion.
    39
    
    Griffin, 483 U.S. at 875
    .
    28
    expectations against CSOSA’s special need to be able to impose such a sanction to
    supervise noncompliant, high-risk probationers.
    We begin by acknowledging that GPS monitoring can be a serious intrusion
    on personal privacy.     Attachment of the GPS device is a trespass on the
    probationer’s person. Having to maintain the device is a chore that somewhat
    curtails the probationer’s activities and freedom of movement. Mr. Jackson’s GPS
    contract, for example, did not allow him to bathe or go swimming, and it required
    him to be inactive for two hours every day while charging the device. Beyond that,
    the Supreme Court has recognized that “individuals have a reasonable expectation
    of privacy in the whole of their physical movements,” including those in the public
    domain.40     Activities carried on in public are not private by definition and,
    generally speaking, no reasonable expectation of privacy attends them; but the
    government’s prolonged, minute-by-minute tracking and recording of all of a
    person’s movements and whereabouts is another matter.41            Such intensive
    40
    Carpenter v. United States, 
    138 S. Ct. 2206
    , 2217 (2018) (emphasis
    added).
    41
    See 
    Jones, 565 U.S. at 430
    (Alito, J., joined by three other Justices,
    concurring in the judgment) (“[R]elatively short-term monitoring of a person’s
    movements on public streets accords with expectations of privacy that our society
    has recognized as reasonable. But the use of longer term GPS monitoring in
    investigations of most offenses impinges on expectations of privacy.”).
    29
    surveillance is unusual and, under normal circumstances, is contrary to the
    ordinary person’s privacy expectations because it has the potential to open “an
    intimate window into a person’s life, revealing not only his particular movements,
    but through them his ‘familial, political, professional, religious, and sexual
    associations.’” 42
    It also must be acknowledged, however, that “nothing of that kind is
    involved in this case.” 43 By itself, CSOSA’s GPS monitoring “just identifies
    locations; it doesn’t reveal what the wearer of the device is doing at any of the
    locations.”44 So far as appears, CSOSA follows internal procedures to ensure that
    GPS monitoring is appropriate, and the tracking data is reviewed solely to
    determine whether supervisees were present at crime scenes or prohibited
    locations, or were violating curfews. When confined to that use, GPS monitoring
    42
    
    Carpenter, 138 S. Ct. at 2217
    (quoting 
    Jones, 565 U.S. at 415
    (opinion of
    Sotomayor, J.)).
    43
    Belleau v. Wall, 
    811 F.3d 929
    , 935 (7th Cir. 2016) (upholding
    constitutionality of statute requiring persons released from civil commitment for
    sex offenses to wear a GPS monitoring device 24 hours a day for the rest of their
    lives).
    44
    
    Id. at 936.
                                             30
    is far less of an intrusion on a supervisee’s privacy than, for example, the
    warrantless search of a private home sanctioned in Griffin.45
    As the Supreme Court emphasized in Griffin and subsequent cases, the
    reasonable privacy expectations of a probationer are not the same as those enjoyed
    by the ordinary citizen; an offender under precautionary and rehabilitative
    supervision on release in lieu of incarceration must expect considerable
    supervisory intrusion on his privacy. Offenders placed on probation in Superior
    Court are informed of what kinds of intrusions to expect. The conditions of Mr.
    Jackson’s probation warned him that he would have to accept (among other
    requirements) home visits by his CSO, drug testing at CSOSA’s discretion, and –
    of particular pertinence to this case – the “program of graduated sanctions” to
    which his conduct on probation might subject him. CSOSA’s regulations and
    procedures require offenders to enter into “accountability contracts” at the outset of
    their probation, in which they expressly acknowledge their probation
    responsibilities and the specified administrative sanctions, including GPS
    monitoring, to which they will be subject for violating the conditions of their
    45
    See Payton v. New York, 
    445 U.S. 573
    , 585 (1980) (“[T]he ‘physical
    entry of the home is the chief evil against which the wording of the Fourth
    Amendment is directed.” (internal quotation marks omitted)).
    31
    supervision.46 Thus, probationers like Mr. Jackson are on notice and agree that
    they will be subject to intensive and intrusive supervision, specifically including
    GPS monitoring, if there is reason to believe they are engaging in criminal activity
    while on probation or otherwise violating the conditions of their release. 47 Mr.
    Jackson’s subsequent, albeit reluctant, acceptance of his GPS monitoring contract
    manifested his awareness that his supervision could include such an intrusion and
    thereby confirmed his “severely diminished expectation of privacy” with respect to
    such monitoring.48
    CSOSA’s disclosed use of electronic monitoring is calculated to be less
    invasive of the probationer’s privacy than prolonged secret surveillance would be.
    46
    See 28 C.F.R. 810.2 (c); Policy Statement 4004, effective November 8,
    2006, “Accountability Contract,” https://www.csosa.gov/wp-content/uploads/bsk-
    pdf-manager/2018/03/4004_accountability_contract_110806.pdf (last visited June
    13, 2019).
    47
    Mr. Jackson’s accountability contract is not included in the record before
    us, however.
    48
    United States v. Newton, 
    369 F.3d 659
    , 665 (2d Cir. 2004) (quoting
    United States v. Reyes, 
    283 F.3d 446
    , 461 (2d Cir. 2002)); see also 
    Samson, 547 U.S. at 852
    (“In Knights, we found that acceptance of a clear and unambiguous
    search condition ‘significantly diminished Knights’ reasonable expectation of
    privacy.’” (quoting 
    Knights, 534 U.S. at 120
    )); United States v. Lambus, 
    897 F.3d 368
    , 410 (2d Cir. 2018) (supervisee’s signing of GPS monitoring agreement “is
    inconsistent with either a legitimate or a reasonable expectation of privacy
    protecting him from constant search via GPS”).
    32
    The probationer’s awareness that his movements will be tracked for a limited
    period of time makes it less likely that the surveillance will be utilized for
    improper purposes or otherwise abused. Knowledge of the monitoring enables the
    probationer to exercise some control over how much of his personal life is
    potentially exposed, and to apply to the court for relief if he believes the
    monitoring is unjustified, excessive, or otherwise objectionable.      Mr. Jackson
    could have exercised the option of applying to the court for relief from the
    monitoring had he wished to do so.49 Alternatively, Mr. Jackson could have
    refused to accept installation of the GPS device, in which case CSOSA would have
    presented the issue to the court itself by moving to revoke or amend Mr. Jackson’s
    probation.
    The infringement on Mr. Jackson’s reasonable privacy expectations must be
    balanced against CSOSA’s legitimate supervisory needs in his case and the extent
    to which the imposition of GPS monitoring promotes the governmental interests in
    deterring recidivism and encouraging Mr. Jackson’s reformation. This side of the
    ledger weighs heavily in favor of the search’s reasonableness. CSOSA’s criteria
    49
    See D.C. Code § 24-304 (a) (2012 Repl. & 2018 Cum. Supp.) (“At any
    time during the probationary term the court may modify the terms and conditions
    of the order of probation, . . . when in the opinion of the court the ends of justice
    shall require . . . .”).
    33
    for placement of supervisees on GPS tracking reasonably limit its use to high-risk
    offenders whose behavior under less intensive supervision demonstrably supports
    the need to monitor them more closely. CSOSA reasonably determined that Mr.
    Jackson met those criteria, as he was on probation for a robbery, he had been re-
    arrested (apparently for another robbery), and he had not been complying with his
    supervisory conditions. CSOSA had ample reason to deem him at high risk of re-
    offending with another violent felony and to find it appropriate to institute GPS
    tracking of his movements to deter him. It cannot plausibly be maintained that the
    intrusion of GPS tracking was disproportionate to the threat Mr. Jackson posed to
    the safety of the community.
    Mr. Jackson’s objection, that CSOSA put him on GPS monitoring at the
    urging of the police because they suspected him of continuing to commit robberies,
    is not well taken. Even if CSOSA’s decision was influenced by that information
    and request, Griffin deemed it “reasonable to permit information provided by a
    police officer . . . to support a probationer search,” 50 and it is well-settled that
    probation officers are permitted to collaborate with the police “as long as the
    probation officers are pursuing legitimate probation-related objectives” in doing
    
    50 483 U.S. at 879-80
    .
    34
    so.51 Here, while the police request was evidently what led CSOSA to consider
    placing Mr. Jackson on GPS monitoring, the record shows that CSOSA did so only
    after determining that he met its own criteria for employing GPS monitoring to
    further the objectives of his probation supervision.
    In addition, the record before us lends no support to Mr. Jackson’s assertion
    that CSOSA put him on GPS monitoring so that the police could “use that
    surveillance for the purpose of its robbery investigation.”52 There is no evidence
    that CSOSA informed the police it had begun tracking Mr. Jackson’s movements,
    and no evidence that the police used his GPS surveillance to investigate his
    potential involvement in robberies other than the one at hand. In the present case,
    of course, Mr. Jackson was not initially identified as a suspect and Detective
    O’Donnell’s initial query of the GPS database did not target him at all; the police
    simply entered the coordinates of the reported robbery and inquired whether
    anyone monitored by CSOSA had been at the scene.
    As the facts of this case illustrate, GPS tracking is a uniquely valuable and
    effective tool for detecting whether a high-risk offender is committing crimes,
    51
    
    Reyes, 283 F.3d at 464
    (citing cases).
    52
    Brief for Appellee at 29 n.18.
    35
    going to prohibited places, or violating curfew, and—because the inquiry of the
    data can be and is selectively limited to those questions—for doing so without
    unnecessarily intruding into the offender’s other activities at all. For the reasons
    identified in Griffin and Hunt, CSOSA’s ability to employ such focused GPS
    monitoring as an intermediate sanction without judicial approval promotes
    legitimate governmental interests in responsive, effective, and commensurate
    supervision of high-risk offenders on probation. As this court recognized in Hunt,
    “sanctions are an alternative to requesting a hearing that ‘may result in . . . changes
    to the conditions of [a probationer’s] release.’” 53 Like the Supreme Court in
    Griffin, we think little if anything would be gained in most cases by “setting up a
    magistrate rather than the probation officer as the judge of how close a supervision
    the probationer requires” from time to time. 54 It is telling that, in the present case,
    although Mr. Jackson complains that CSOSA did not seek judicial approval of its
    decision to put him on GPS monitoring, he has not argued that the decision was
    unjustified by his behavior on probation, nor has he identified any reason a judge
    might have disagreed with it in his case. As we have said, judicial review of a
    
    53 109 A.3d at 623
    (quoting 28 C.F.R. § 810.3(a) (2014)).
    
    54 483 U.S. at 876
    .
    36
    questionable decision to initiate GPS monitoring is available to a probationer. Mr.
    Jackson did not seek such review.
    Although a court may have reason in some cases to make compliance with
    GPS monitoring an express condition of probation at the time the court imposes
    sentence, such an express condition is not a constitutional prerequisite for the
    probationer to be subjected to a monitoring requirement if his behavior on
    probation calls for it as a reasonable sanction.55 The need for a GPS monitoring
    requirement is not something that can be predicted accurately at the time of
    sentencing; unanticipated circumstances may arise and justify CSOSA’s
    employment of that tool as an intermediate and hopefully temporary sanction.
    In our view, the limited nature and degree of the intrusion by GPS
    monitoring on Mr. Jackson’s privacy was outweighed by the extent to which that
    intrusion was needed to promote the government’s legitimate and important
    interests in the effective supervision of a high-risk probationer. Like the Supreme
    Court in Griffin, we therefore conclude that CSOSA’s placement of Mr. Jackson
    on GPS monitoring pursuant to its regulations governing probationers was a
    55
    In Griffin, for example, the Court upheld the warrantless search of a
    probationer’s home even though no condition of probation authorized it.
    37
    reasonable search within the meaning of the Fourth Amendment. It is on this
    premise that we now turn to consider the ruling that the MPD’s access to Mr.
    Jackson’s GPS tracking data violated his Fourth Amendment rights because he
    retained an undiminished expectation of privacy in that data with respect to the
    police.
    B. CSOSA Did Not Violate Mr. Jackson’s Reasonable Expectation of
    Privacy by Sharing His GPS Data with the Police for Legitimate Compliance-
    Related Purposes.
    In concluding that the police violated Mr. Jackson’s reasonable expectation
    of privacy in his GPS data, the motions judge relied on the Supreme Court’s
    analysis in Knights of a warrantless search of a probationer’s residence by the
    police.    Because that search was independent of the probation department’s
    exercise of supervision over the probationer, it was not justified by Griffin’s
    “special needs” rationale. The Supreme Court upheld the police search in Knights
    on a different rationale, one grounded on the “salient” fact that a condition of Mr.
    Knights’s probation explicitly required him to submit to a search at any time,
    without cause, by either a probation officer or a law enforcement officer.56 By
    virtue of his knowing acceptance of that search condition, the Court held, Mr.
    
    56 534 U.S. at 118
    .
    38
    Knights’s reasonable expectation of privacy as a probationer was so “significantly
    diminished” that the police constitutionally could search his home without a
    warrant based on “no more than reasonable suspicion” of criminal activity there.57
    In the present case, the judge noted that Mr. Jackson’s GPS contract with
    CSOSA contained “no clear and unambiguous search condition allowing MPD
    access.” The conditions of Mr. Jackson’s probation were “similarly devoid of any
    reference to the MPD.” Consequently, the judge stated, Mr. Jackson’s “reasonable
    expectation of privacy as to the MPD was not diminished” (emphasis added). On
    that premise, the judge proceeded to balance the intrusion of GPS monitoring on
    Mr. Jackson’s entirely undiminished expectation of privacy in his movements
    against “the MPD’s general interest in criminal investigation,” inasmuch as “it was
    the MPD, and not CSOSA, who carried out the search in the course of
    investigating a crime.” The judge concluded that “[b]ecause the MPD’s search of
    57
    
    Id. at 121.
    Although Mr. Knights’s probation condition purported to
    authorize searches without any individualized suspicion at all, the Court found it
    unnecessary to address the constitutionality of a suspicionless search because the
    search in the case before it was supported by reasonable suspicion. 
    Id. at 120
    n.6.
    Later, in Samson, the Court held that the Fourth Amendment does not prohibit a
    police officer from conducting a suspicionless search of a parolee subject to a
    release condition explicitly authorizing such a 
    search. 547 U.S. at 847
    . In arriving
    at that conclusion, the Court observed that “parolees have fewer expectations of
    privacy than probationers, because parole is more akin to imprisonment than
    probation is to imprisonment.” 
    Id. at 850.
                                            39
    Jackson’s GPS location information was neither based on any level of
    individualized suspicion[58] nor conducted pursuant to a clear and unambiguous
    search condition, Jackson’s intact reasonable expectation of privacy as to the MPD
    outweighs the government’s interest. . . .      The MPD search was therefore
    unreasonable under the Fourth Amendment.”
    We perceive several questionable features of this analysis. For one thing,
    the judge’s weighing does not seem to take into account the quite limited scope of
    the actual intrusion by the police on Mr. Jackson’s privacy, nor the fact that once
    the police discovered he was at the scene of the robbery, they had ample
    individualized suspicion that he committed the robbery – points to which we shall
    return below.   For another thing, although the Supreme Court relied on the
    existence of an explicit search condition to uphold the search of a probationer’s
    residence in Knights, it does not necessarily follow that (as the motions judge
    58
    The judge noted that the police “made no effort to determine whether
    there was a sufficiently high probability that Jackson committed the robbery”
    before turning to the GPS records of CSOSA’s monitored supervisees “as a tool for
    criminal investigation.”
    40
    appears to have reasoned) such an explicit condition is always necessary to
    diminish a probationer’s reasonable expectation of privacy in his movements. 59
    Most important, we think the judge’s analysis overlooks a critical distinction
    between Knights and the present case. Unlike in Knights, the intrusion on Mr.
    Jackson’s expectation of privacy to acquire the incriminating evidence was
    performed, in the first instance, in the course of his probationary supervision. It
    was CSOSA, not the police, that attached the device and collected Mr. Jackson’s
    GPS data for its own compliance-related purposes, in what we have concluded was
    a constitutional search; and (again, unlike in Knights) it was CSOSA’s decision to
    grant the police access to that collected data. We therefore think the Fourth
    Amendment issue is properly framed differently from the way the motions judge
    framed it. The constitutional issue in our view is whether Mr. Jackson had an
    objectively reasonable expectation that CSOSA would not share his GPS data with
    the MPD. For the reasons that follow, we conclude that such an expectation would
    not have been reasonable.
    59
    The judge drew the dubious conclusion that “it is not the individual’s
    status as a probationer that diminishes his expectation of privacy. Rather, it is the
    search condition, permissible due to probationer status, that diminishes the
    individual’s expectation of privacy.” But see 
    Knights, 534 U.S. at 119
    (“Inherent
    in the very nature of probation is that probationers do not enjoy the absolute liberty
    to which every citizen is entitled.” (quotation marks and citations omitted)).
    41
    CSOSA granted the MPD access to its supervisees’ GPS monitoring data
    (and received access to the MPD’s locational and temporal data pertaining to
    crimes, arrests, and other law enforcement activities) pursuant to a longstanding
    information-sharing agreement between the two agencies. Their Memorandum of
    Understanding (MOU), an exhibit in the proceedings below, explains that CSOSA
    and the MPD “share a common mission to reduce and prevent crime,” and that a
    purpose of their two-way automated and routine data sharing arrangements is “to
    enhance CSOSA’s ability to prevent supervised offenders from engaging in
    criminal activity, thereby reducing recidivism and improving public safety, in
    accord with the agency’s mission.” The MPD’s detection of criminal activity by
    CSOSA’s supervisees and enforcement of the law against them serves CSOSA’s
    supervisory goals as well as the MPD’s own law enforcement ends. To help
    achieve CSOSA’s supervisory goals, the MPD’s data-sharing commitments to
    CSOSA extend to providing electronic notification whenever one of CSOSA’s
    supervised offenders is “matched to an MPDC arrest event,” and in other ways
    enabling CSOSA personnel to determine whether information and intelligence in
    police databases “will affect an offender’s supervision level or other aspects of
    CSOSA case management.”
    42
    As CSOSA and the MPD agreed in the MOU, their data sharing is subject to
    their compliance with applicable District of Columbia and federal law governing
    the confidentiality of the information, specifically including (as pertinent here) the
    Privacy Act, 5 U.S.C. § 552a (2014).60        Thus, the MOU provides that data-
    connectivity is contingent on CSOSA’s publication of a “routine use” Privacy Act
    notice in the Federal Register stating that its records may be disseminated to law
    enforcement agencies “to assist in the general crime prevention and detection
    efforts of the recipient agency or to provide investigative leads to such agency.”
    Accordingly, in 2006, CSOSA published a notice in the Federal Register stating it
    would treat as a routine use the disclosure of “electronic monitoring information,”
    including “Global Positioning System (GPS) data,” to the MPD and other law
    enforcement agencies that “require[] information relevant to a civil or criminal
    investigation to the extent necessary to accomplish their assigned duties unless
    60
    The Privacy Act provides, in pertinent part, that “[n]o agency shall
    disclose any record which is contained in a system of records by any means of
    communication to any person, or to another agency, except . . . with the prior
    written consent of[] the individual to whom the record pertains, unless disclosure
    of the record would be . . . (3) for a routine use as defined in subsection (a)(7) of
    this section and described under subsection (e)(4)(D) of this section.” 5 U.S.C. §
    552a(b) (emphasis added). The term “routine use” is defined to mean, “with
    respect to the disclosure of a record, the use of such record for a purpose which is
    compatible with the purpose for which it was collected.” 
    Id. § 552a(a)(7).
    Subsection (e)(4)(D) provides for agency publication in the Federal Register of
    “each routine use of the records contained in the system, including the categories
    of users and the purpose of such use.”
    43
    prohibited by law or regulation” or “to assist in the general crime prevention and
    detention efforts of the recipient agency or to provide investigative leads to such
    agency.” 61
    CSOSA made no secret of its sharing of GPS monitoring data with the
    police. As previously noted in Section II.A of this opinion, CSOSA publicized on
    its website the MPD’s use of its GPS tracking data to “aid in suspect
    apprehension.”
    In view of CSOSA’s established and publicly-declared practice of sharing its
    GPS tracking data with the MPD as a routine use permitted by the Privacy Act, it is
    difficult to see how Mr. Jackson could have expected otherwise. CSOSA was
    under no legal obligation to withhold its supervisees’ GPS tracking data from the
    61
    71 Fed. Reg. 58, pp. 15177-78 (Mar. 27, 2006); see also 74 Fed. Reg.
    158, pp. 41689-90 (Aug. 18, 2009). The release of parole supervision records to
    further a criminal investigation has been held to qualify as a routine use under the
    Privacy Act, see United States v. Miller, 
    643 F.2d 713
    , 715 (10th Cir. 1981), and it
    is not suggested that probation supervision records should be treated differently in
    this respect. We think it clear that CSOSA’s disclosure of the GPS tracking data to
    the MPD and other law enforcement agencies is for purposes that are “compatible”
    with the purposes for which CSOSA collected that data. Cf. Kimberlin v. United
    States Dep’t of Justice, 
    788 F.2d 434
    , 437-38 (7th Cir. 1986) (upholding disclosure
    of federal prison inmate’s information to probation officer as a routine use under
    the Privacy Act, because “[a] probation officer is clearly a law enforcement official
    as the term is ordinarily used”).
    44
    police. It did not tell Mr. Jackson it would do so; nor does he claim to have
    received such an assurance of confidentiality from the court or any other source.
    In point of fact, as far as we are aware, nothing in the record indicates Mr. Jackson
    actually was surprised to learn CSOSA had shared his GPS tracking data with the
    MPD. If anything, Mr. Jackson’s dismayed remark to his CSO – that “he wouldn’t
    be able to do anything” after the GPS device was attached to his ankle – suggests
    he foresaw the possibility.
    In any event, an expectation on Mr. Jackson’s part that CSOSA would not
    voluntarily share his GPS data with the police for their mutual, compliance-related
    purposes would have been objectively unreasonable.         A primary objective of
    probationary supervision is “the protection of society from future criminal
    violations.”62   Cooperation with and enlistment of the police are means of
    accomplishing that objective. A probation officer is, as the Supreme Court has put
    it, “a peace officer, and as such is allied, to a greater or lesser extent, with his
    fellow peace officers.” 63 An offender on probation “cannot pretend ignorance” of
    that fact, and “[a]bsent some express or implied promise to the contrary, he may
    62
    Washington v. United States, 
    8 A.3d 1234
    , 1235 (D.C. 2010).
    63
    Fare v. Michael C., 
    442 U.S. 707
    , 720 (1979).
    45
    also be charged with knowledge that the probation officer is duty bound to report
    wrongdoing by the probationer when it comes to his attention, even if by
    communication from the probationer himself.”64
    The same principle applies to sharing evidence of a probationer’s possible
    wrongdoing, including his whereabouts while under supervisory GPS tracking. As
    a general rule, courts have held that law enforcement agencies do not violate
    reasonable expectations of privacy or Fourth Amendment limitations by sharing
    evidence and information they have acquired in lawful searches and seizures with
    other law enforcement agencies for legitimate law enforcement purposes.65 More
    to the point, it is well-settled that, because “the objectives and duties of probation
    officers and law enforcement personnel are often parallel and frequently
    intertwined[,] the law permits cooperation between probation officers and other
    law enforcement officials so that they may work together and share information to
    64
    Minnesota v. Murphy, 
    465 U.S. 420
    , 432 (1984) (internal punctuation and
    citations omitted).
    65
    See, e.g., United States v. Jenkins, 
    496 F.2d 57
    , 73 (2d Cir. 1974)
    (approving of local police allowing federal agents to examine, for a bank robbery
    investigation, the serial numbers of dollar bills that the local police collected from
    the appellant at the time of his arrest on a gun charge); United States v. Gargotto,
    
    476 F.2d 1009
    , 1014 (6th Cir. 1973) (“Evidence legally obtained by one police
    agency may be made available to other such agencies without a warrant, even for a
    use different from that for which it was originally taken.”).
    46
    achieve their objectives.” 66 In Griffin the Supreme Court clearly implied, and
    other courts have held, that probation officers may share the lawfully-obtained
    fruits of probation searches with the police even if it would not have been lawful
    for the police to conduct the searches themselves. 67
    One of CSOSA’s legitimate objectives is to detect the presence of its high-
    risk supervisees at the scenes of criminal activity by comparing their GPS tracking
    data with crime location data supplied by the MPD for that purpose.
    Individualized suspicion linking particular supervisees to particular crimes is not a
    precondition for CSOSA to conduct such narrowly targeted data searches; the point
    66
    
    Reyes, 283 F.3d at 471
    ; see also United States v. McFarland, 
    116 F.3d 316
    , 319 (8th Cir. 1997) (stating that “[p]arole and police officers may work
    together, . . . provided the parole officer is pursuing parole-related objectives”);
    United States v. Martin, 
    25 F.3d 293
    , 296 (6th Cir. 1994) (“[P]olice officers and
    probation officers can work together and share information to achieve their
    objectives.”).
    67
    See, e.g., 
    Lambus, 897 F.3d at 407
    , 409, 412 (approving state parole
    officer’s sharing of GPS tracking information with federal law enforcement agents
    for a federal investigation because such cooperation was “rationally and reasonably
    related to” the parole officer’s interest in preventing parolees “from engaging in
    new criminal activity”); 
    Newton, 369 F.3d at 668
    (“[I]n United States v. 
    Reyes, 283 F.3d at 463-64
    , we approved coordinated activities between probation/parole
    officers and other law enforcement officials in furtherance of legitimate
    supervision objectives even though the specific conditions of supervision there at
    issue provided for residential intrusions only by a probation officer, with no
    mention of other law enforcement officials.”).
    47
    of GPS monitoring is to discourage its supervisees from engaging in criminal
    activity and to discover whether grounds for suspicion exist. When the monitoring
    implicates a supervisee in criminal activity, nothing in the Fourth Amendment
    forbids CSOSA from reporting that information to law enforcement. Presumably,
    if Mr. Jackson’s CSO had learned from his GPS tracking data before the police did
    that Mr. Jackson was present when Mr. Parker and Ms. Pleasant were robbed at
    gunpoint, the CSO would have so informed the police. None of that would have
    violated Mr. Jackson’s reasonable expectations of privacy in his whereabouts.
    What happened in this case is not materially different – CSOSA allowed the
    police to access its GPS tracking database to obtain directly the same limited
    information regarding its monitored supervisees’ presence at crime locations that
    CSOSA could obtain and hand over to the police. We see no reason to question
    CSOSA’s judgment that this furthered its legitimate supervisory objectives. As
    this very case illustrates, the police may be able to take appropriate law
    enforcement action more quickly, efficiently, and effectively than CSOSA can.
    There is no evidence in this case that CSOSA’s sharing of its GPS tracking
    data with the MPD exposes monitored supervisees to a materially greater intrusion
    on their privacy, or to a materially different use of the information gained. The
    48
    police did not use Mr. Jackson’s GPS data to pry into his intimate or private affairs
    or the details of his personal life. They sought and obtained limited information
    and properly used it for law enforcement purposes. At the outset, the police sought
    to learn only whether any monitored supervisee was at the scene of the crime when
    it occurred. The police learned absolutely nothing about any supervisees who were
    not at the scene; their privacy was not invaded in any way. As for Mr. Jackson, the
    GPS data revealed only that he was at the crime scene – a public space in which he
    had no reasonable expectation of privacy.             That information provided
    particularized suspicion (if not, indeed, probable cause) for the police to believe
    Mr. Jackson was one of the robbers, and ample justification for the police to track
    his public movements in the minutes immediately following the crime so that he
    would not escape or dispose of evidence. 68       Mr. Jackson did not possess a
    68
    Although we do not think the police were obliged to apply for a search
    warrant in order to track Mr. Jackson’s flight after they discovered he was present
    at the scene of the robbery, we note that the existence at that point of exigent
    circumstances provided an alternative justification for proceeding without a
    warrant. See 
    Carpenter, 138 S. Ct. at 2223-24
    (explaining that although the
    government will “generally” need a warrant to access cell-site location information
    comparable to GPS data, the exigencies of the situation may render it objectively
    reasonable to collect the information without a warrant; “[s]uch exigencies include
    the need to pursue a fleeing suspect, . . . or prevent the imminent destruction of
    evidence”).
    49
    reasonable expectation that those movements would be private.69 The police use of
    his GPS data did not extend beyond that tracking. While long-term GPS tracking
    impinges significantly on a person’s expectation of privacy in his movements,
    there was nothing long-term about the police tracking of Mr. Jackson; it was as
    brief as it could possibly have been. Although the police learned that Mr. Jackson
    fled into an apartment (it is unclear whether they knew or had reason to believe it
    was Mr. Jackson’s residence), the tracking disclosed nothing about his activities
    inside it.   In short, any intrusion by the police on Mr. Jackson’s reasonable
    expectation of privacy was de minimis, in our view, and far outweighed by its
    public benefits. Mr. Jackson has no grounds to complain that the police, by
    resorting to his GPS data in the immediate aftermath of the armed robbery, were
    able to arrest him more swiftly and recover corroborative physical evidence that
    otherwise might have been lost.       If that was so, it only underscores the
    reasonableness of CSOSA’s sharing of the data with the police.
    Mr. Jackson argues that CSOSA’s sharing of its GPS tracking data with the
    police for use in law enforcement is at odds with the Supreme Court’s decision in
    69
    See United States v. Knotts, 
    460 U.S. 276
    , 281 (1983) (“A person
    traveling in an automobile on public thoroughfares has no reasonable expectation
    of privacy in his movements from one place to another.”).
    50
    Ferguson v. Charleston.70 We do not agree. In Ferguson, the Court held that a
    public hospital violated its patients’ Fourth Amendment rights if, in testing them
    for illegal drug use as part of their medical care, the hospital did so with the
    undisclosed objective of obtaining incriminating evidence and sharing it with law
    enforcement for purposes of prosecuting the patients. That case is not comparable
    to this one. The persons subject to the searches in Ferguson were “typical”
    hospital patients with typical, undiminished privacy expectations.      The Court
    recognized that they reasonably expected the hospital would not voluntarily share
    their personal and private medical test results with outsiders for a non-medical use
    such as criminal prosecution unless the hospital had their informed consent to do
    so.71        In contrast, CSOSA’s supervisees are convicted probationers with
    significantly diminished expectations of privacy in their activities; they are aware
    CSOSA collects their GPS tracking data with a law enforcement objective; and
    having that awareness, they cannot reasonably expect CSOSA to withhold the GPS
    70
    
    532 U.S. 67
    (2001).
    71
    
    Id. at 78.
    Not insignificantly, however, the Court distinguished
    circumstances in which state hospital employees are legally obligated to report
    evidence of criminal conduct acquired in the course of providing medical care.
    The Court noted that the existence of reporting laws might bear on the patients’
    reasonable expectations of privacy in their personal information. 
    Id. at 78
    n.13,
    80-81
    51
    data from other agencies that share CSOSA’s objective and will utilize the data to
    further it.
    We conclude that CSOSA did not violate Mr. Jackson’s reasonable
    expectation of privacy by granting the police access to his GPS tracking data in
    furtherance of their mutual law enforcement objectives.         The limited police
    utilization of that access comported with the reason CSOSA granted it and did not
    unreasonably intrude on Mr. Jackson’s privacy. We therefore conclude that Mr.
    Jackson’s Fourth Amendment rights were not violated.
    We emphasize that we have considered in this opinion only whether the
    police violated Mr. Jackson’s Fourth Amendment rights by the limited inspection
    and use they actually made of his GPS tracking data. We uphold a narrowly
    tailored resort by the police to the GPS data in the absence of articulable suspicion
    – the same check to determine whether a monitored probationer was at the scene of
    the crime when it occurred that CSOSA itself routinely and permissibly performs,
    likewise without articulable suspicion. In doing so, we recognize the sensitivity of
    GPS tracking information and do not dismiss privacy concerns about its
    susceptibility to possible abuse by overzealous investigators. But no abuse is
    revealed by the record before us in this case and, particularly when the question is
    52
    a constitutional one, “[c]ourts should not decide more than the occasion
    demands.”72    We therefore refrain from discussing whether the police
    hypothetically would violate the Fourth Amendment if they were to explore
    CSOSA’s GPS data more extensively or without the valid law enforcement
    purpose present in this case.
    III.
    For the foregoing reasons, we reverse the order of the Superior Court
    granting Mr. Jackson’s motion to suppress electronic and tangible evidence and
    remand for further proceedings.
    72
    District of Columbia v. WICAL Ltd. P’ship, 
    630 A.2d 174
    , 182 (D.C.
    1993) (quotation marks and citation omitted).