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Carpenter v. U.S . concerns the conviction of Timothy Carpenter for multiple armed robberies of Radio Shacks and T–Mobile stores in 2010 and 2011. A key piece of evidence used in the government’s case against Carpenter was historical cell site location information (“CSLI”) records showing Carpenter’s phone, and consequently Carpenter, was located “within a half-mile to two miles of the location of each of the robberies around the time the robberies happened.” The 127 days’ worth of CSLI was obtained from various wireless service providers using a 2703(d) “articulable facts” court order pursuant to the Stored Communications Act, a federal statutory privacy law. Carpenter successfully appealed his conviction all the way to the Supreme Court.
In his initial brief to the Court, Carpenter argues that law enforcement agents may not acquire CSLI records covering a “longer-term” period of time unless they first obtain a Fourth Amendment search warrant. Carpenter’s argument relies heavily on a mosaic theory of the Fourth Amendment. One of the nation’s foremost Fourth Amendment scholars, Orin Kerr, coined the term mosaic theory and describes it this way:
Under the mosaic theory, searches can be analyzed as a collective sequence of steps rather than as individual steps. Identifying Fourth Amendment searches requires analyzing police actions over time as a collective “mosaic” of surveillance; the mosaic can count as a collective Fourth Amendment search even though the individual steps taken in isolation do not.
In Carpenter’s case, law enforcement obtained CSLI data about Carpenter’s whereabouts over a four month period. Picking out CSLI data for one day within this four month period won’t tell you much about him, but when the CSLI for the entire 127-day period is aggregated, dissected, and analyzed, it will tell you very much. It shows a “pattern of life” – CSLI aggregated over time can be used to construct a detailed picture of where a person has been, who the person has been with, and what the person may have been doing. The mosaic picture tells you so much about the person that the Fourth Amendment is implicated, requiring law enforcement to first obtain a warrant before requesting the underlying CSLI data from wireless providers.
The mosaic theory of the Fourth Amendment was introduced by the D.C. Circuit Court of Appeals in U.S. v. Maynard, and further explored by the Supreme Court in U.S. v. Jones, its review of Maynard. In Jones, law enforcement agent’s tracked a car’s movements for 28 days using a GPS device. The Supreme Court held that the government's attachment of a GPS device to the vehicle, and its use of that device to monitor the vehicle's movements, constituted a search under the Fourth Amendment. The Court reasoned that the placing of the GPS device on the car was a physical intrusion – a physical trespass on the “effects” of the car – and thus a “search” within the meaning of the Fourth Amendment.
There are two keys to understanding why Carpenter relies on a mosaic theory argument in his brief. The first key is what the majority opinion in Jones did not do. The majority did not decide whether governmental surveillance of Jones for a 4–week period “through electronic means, without an accompanying trespass, is an unconstitutional invasion of privacy” because the facts of the case did not require such an answer. The facts of Carpenter v. U.S., on the other hand, do require such an answer from the Court.
Second, the concurring opinions in Jones provide a glimpse of how some Justices will attempt to answer the question presented in Carpenter. Justice Sotomayor, in her concurrence, examines the question whether surveillance using electronic means and absent a trespass should constitute a search under the Fourth Amendment. Her examination was not in-depth, but it does provide an outline. She explains that in situations involving merely the transmission of electronic signals without a trespass, a Fourth Amendment search occurs when the government violates a subjective expectation of privacy that society recognizes as reasonable. She further explains that for cases involving electronic surveillance, the unique attributes of the surveillance “will require particular attention.” Like the GPS monitoring in Jones, the historical CSLI records at play in Carpenter “generate[] a precise, comprehensive record of a person’s public movements that reflects a wealth of detail about her familial, political, professional, religious, and sexual associations.” According to Justice Sotomayor, the Court, when reviewing Carpenter, will have to consider whether there is an expectation of privacy in the intimate details that can be gleaned from the aggregate CSLI.
Carpenter’s mosaic theory argument in his brief tracks the outline provided by Justice Sotomayor’s concurrence in Jones, and it’s a good argument. It’s one that has been debated extensively since the Supreme Court decided Jones. Without a doubt, the Court will have to address the mosaic theory of the Fourth Amendment when it decides Carpenter. Will it adopt the theory? This is the where the mosaic theory is problematic. It is difficult for courts to apply in actual cases. How should it be applied? Carpenter concerns the collection of CSLI over a 127-day period. At what point does law enforcement’s collection of CSLI trigger the Fourth Amendment? Which is more important when making such an analysis, the quantity of information or the quality of information. Or is it the number of consecutive days’ worth of information? How would governmental agents know whether their actions comply with or violate the standard? These are issues that make the mosaic theory so difficult. Eventually, we’ll see if the Supreme Court agrees.
