The Supreme Court ruling in Carpenter and its implications for law enforcement in the digital age


In its biggest Fourth Amendment case of at least this year, the Supreme Court’s 5-4 ruling came down June 22 in Carpenter v. United States, ordering that collection of historical cell site location information, or CSLI, should “generally” require police to get a warrantAlong with many other organizations, Restore The Fourth had recognized how significant this case was likely to be, and we filed an amicus brief in the case. We argued that:

  • Despite the so-called “third-party doctrine”, even when people disclose their information to third parties, that should not mean that they do not have a reasonable expectation of privacy;
  • Over time, cell site location information will become more revealing, thanks to increased density of tower locations and the increased power of computers to algorithmically parse information;
  • Police warrantless use of CSLI comes with an unusually high risk of abuse.

The majority opinion, written by Chief Justice Roberts and joined by Breyer, Ginsburg, Kagan and Sotomayor, agreed at least with the first two of our points.

Amy Howe, writing for SCOTUSBlog, ably summarizes the facts of the case:


Timothy Carpenter, who was convicted and sentenced to almost 116 years in prison for his role in a series of armed robberies in Ohio and Michigan. Law-enforcement officials used cell-site records from his cellphone provider to place him in the vicinity of the crimes, but Carpenter argued that the jury should not hear about those records because the government had not obtained a warrant for them. A federal appeals court upheld his conviction, explaining that the government was not required to seek a warrant because Carpenter could not have expected cellphone records maintained by his service provider to remain private. This morning the Supreme Court reversed that ruling.


Here is Restore The Fourth’s Litigation Working Group chair, Mahesha Subbaraman, being interviewed on the case: https://www.kare11.com/article/news/scotus-adopts-new-rules-for-cellphone-tracking/89-566775789

When A Warrant Is Required

Perhaps the most confusing part of the ruling is that Chief Justice Roberts insistently declares that the circumstance where a criminal suspect has a reasonable expectation of privacy in records held by a third party will be “rare”, and that therefore requiring a warrant for searches of historical CSLI will not disrupt a broad swath of police practice. Though Roberts may have an expectation of rareness, in reality searches of historical CSLI are common, and are bound by the Carpenter opinion even if Roberts feels the need for a rhetorical flourish as to their rareness. For that reason, the main dissent, authored by Kennedy, is right to say that the majority’s “reinterpretation of Miller and Smith will have dramatic consequences for law enforcement, courts, and society as a whole.” The fact that it is common practice for government to requisition financial or telephonic information without bothering with the formality of a warrant is a bug, not a feature, and correcting that is part of the process of restoring the Fourth.

The majority opinion regards historical CSLI as categorically different from the kind of financial records at issue in Miller, because historical CSLI is a long-term record of people’s movements over time; but this effectively carves out a subset of particularly intrusive metadata and affords it warrant protection, rather than maintaining the content/metadata distinction that has underpinned Fourth Amendment law since the 1970s – as Kennedy’s dissent puts it, it “draws an unprincipled and unworkable line between cell-site records on the one hand and financial and telephonic records on the other.” The line will likely be much litigated.

Responding to the time limit in the case before it, the Court declared that the government asking for seven days of historical CSLI, but actually receiving only two, would trigger a warrant requirement, implicitly indicating that asking for six days’ worth would not – perhaps, even if what the government actually received was six days’ worth. This is clearer than simply saying, as courts tend to do in the area of the Fourth Amendment, that whether warrant protection is triggered “depends on the totality of the circumstances”, but not by much. Why seven days of requested data in particular? Because Carpenter says so. This rule, and the ruling more broadly, offers little to those who thirst for clarity and administrability in Supreme Court rulings.

Two Theories of Why a Warrant is Required

A matter of deep interest to court-watchers was not only whether warrant protection would be given to historical CSLI, but why. A key division on the Court continues to be between those who are comfortable with continuing to develop the sixty-year-old Katz “reasonable expectations of privacy” test, which determines whether something is a search on the basis of whether the person searched has had an “expectation of privacy” violated that “society is prepared to recognize as reasonable”; and those who prefer to examine the question of whether something is a search exclusively through a property-focused lens, to understand whether a “trespass” can be deemed to have occurred.  This particular opinion showcases that split, with the Court’s liberal Justices, plus Roberts, in the Katz camp, and Alito, Gorsuch, Kennedy and Thomas, in their different ways, in the property-rights camp. At Restore The Fourth, we don’t believe that either the Katz approach or the property-rights approach is wrong. Either can lead to a restoration of people’s privacy as against government searches and seizure; the debate on the Court between these camps has so far been immensely productive of increased protections.

Thomas dissents separately, he says, because in law, historical CSLI relating to Carpenter’s movements does not belong to him; if it does not belong to him, then it cannot be deemed a “paper or effect” of Carpenter’s; and therefore he cannot claim a violation of the Fourth Amendment with respect to him. The FCC does say that “to the extent that” CSLI should be considered property, it should be treated as the property of the customer, not the carrier. Thomas declares that this is “weak”, and Alito, in a dissent joined by Thomas, argues that the Founders did not envision a situation where the ordinary processes of requiring documents to be produced in a criminal proceeding (subpoena duces tecum) would be subject to the requirements of a warrant.

The difficulty with drawing originalist analogies is that you get to pick and choose the analogy. Thomas sketches out a situation where of course the Founders accepted that the Fourth Amendment would not be relevant to subpoenas of documents from third parties. He chooses not to sketch out a situation where the Founders are confronted by a warehouse, owned by a trading company, containing physical documents attesting to the minute-by-minute whereabouts of every resident of the American colonies, and accessible on a trivial showing by agents of the Crown. Had he chosen that analogy, then of course the Founders would have thought that the powers of the Crown over the colonials were thereby rendered excessive. Through choice of analogy, originalism sometimes risks becoming the same exercise in projection of contemporary assumptions over the Constitution that originalists decry.

We can see the difference in choice of analogy in the profound and interesting Gorsuch dissent. Gorsuch plainly and intelligently skewers the limitations of both a “king always wins” rule as envisioned by broad application of Smith and Miller, and the vagueness and plasticity of the majority opinion’s limiting language based on the Katz “reasonable expectation of privacy” test:

“At what point does access to electronic data amount to “arbitrary” authority? When does police surveillance become “too permeating”? And what sort of “obstacles” should judges “place” in law enforcement’s path when it does? We simply do not know.”

Gorsuch finds that Carpenter has, if not a full right to treat CSLI as his own property, then at least enough of a property interest for Fourth Amendment purposes that he can claim that his “papers or effects” were searched. Without entirely dismissing Katz, he charts out a method for applying a property-based theory of the Fourth Amendment whereby state legislatures’ efforts to protect people’s privacy in the data held about them by third parties could be construed by courts to create property rights in that data. He uses Ex parte Jackson (1878), a case relating to the privacy of letters sent via USPS, to indicate that there is some “constitutional floor” of protection in such records below which state laws cannot go, for example by declaring that they can be seized and searched at will. And, as he has done in prior opinions, he uses the eighteenth-century analogy of the duties of a bailee as a way of dealing with the problems caused by the third-party doctrine that would allow an originalist-minded Court to accept a property interest in both CSLI and in business records held by third parties more generally.

Evidently, Gorsuch’s Fourth Amendment analysis has not yet persuaded a substantial portion of the Court to join him; but just as Sotomayor’s innovative concurrence in Jones (2011) now underpins the majority opinion in Carpenter, it would not be surprising if Gorsuch’s theory of how the Fourth Amendment should develop in the light of technological change were to become significantly more influential in the years ahead.

Implications for National Security Surveillance

Justice Roberts emphasized that the holding that a warrant was required “does not consider other collection techniques involving foreign affairs or national security.” Though these words sound cautious, they are potentially a landmine laid under the ramifying superstructure of the surveillance state. First, of course, he is not saying that Carpenter’s reasoning could not validly apply to the oceans of metadata collected by the surveillance agencies, only that such collection was not before the Court in this ruling. Second, the emphasis is that Carpenter does not consider other collection techniques involving foreign affairs or national security, which (it will surely shortly be argued) most naturally suggests that the Court does think a warrant should apply to historical CSLI collection in particular even when it involves foreign affairs or national security, when (assumedly, given other precedents) that collection occurs in the United States.

This matters immensely, because the communications metadata of an unknown number of Americans, but probably numbering in the millions, is being collected under the authority of Section 702 of the FISA Amendments Act. The Americans being collected upon are either contacts of, or are talking about, one of over 100,000 “targets”, who can be any foreign national whose communications might be of intelligence interest to the United States – they don’t have to be, and mostly are not, terrorists. Whether, in a future ruling, the Supreme Court will be willing to explicitly rule that such collection requires a warrant depends in large part on the ability of plaintiffs in surveillance cases to resolve the aching problem of standing – i.e., to be able to prove to the Court’s satisfaction that, as US citizens, they have in fact been surveilled by a surveillance agency; and that surveillance of their historical CSLI in particular has caused them a harm that the Court is prepared to recognize.

The FBI in particular has a lot of reason to worry. The ruling may not explicitly overrule Smith v. Maryland, the phone metadata case that underpins the legal justification for mass surveillance of telephonic metadata; but it signals that a majority of the Supreme Court thinks that there are major problems in applying the reasoning of Smith to police surveillance cases.


Carpenter is a hugely significant ruling in the Supreme Court’s Fourth Amendment jurisprudence. For the first time, the Court has clearly recognized that citizens have a cognizable interest in a particular type of records about them held by third parties. But, as with Jones, it is important not so much for adding clarity, as for marking a step in the Court’s circuitous journey towards a clearer understanding of how law enforcement use of data affects our individual freedoms. Thanks to Chief Justice Roberts’ leadership in extending privacy protections to data generated by new technologies, and to the recent additions of Sotomayor and Gorsuch as important and very different voices willing to rein in police surveillance, we have reason for hope. We should expect a continued flood of Fourth Amendment litigation, and continued conflicts as the Court wrestles with why and how to maintain individual privacy in the digital way, in a discussion that in both its content and its results, currently far outshines the work product of the other two branches of government.