The pending challenges in ACLU v. Clapper and Klayman v. Obama (now on appeal before the Second Circuit and D.C. Circuit, respectively) raise the question of whether the mosaic theory supports the Fourth Amendment’s application to the NSA’s bulk collection of telephony metadata under Section 215 of the USA PATRIOT Act.   Under this theory, the aggregation of vast amounts of metadata should be considered a “search” within the meaning of the Fourth Amendment because it can reveal a great deal about a person’s life, even if each piece of data might reveal little when viewed in isolation.

The mosaic theory provides an opportunity to adopt the Fourth Amendment to the privacy intrusions accompanying rapid technological change.  It also provides a means of mitigating asymmetries between government and individual interests associated with the collection and protection of information.  Just as the mosaic theory has helped the government maintain secrecy over information that might otherwise be in the public domain, it represents an opportunity to protect individual privacy in an age of big data.

In Klayman, District Judge Richard Leon found that the mosaic theory supported the Fourth Amendment’s application, explaining that “records that once would have revealed a few scattered tiles of information about a person now reveal an entire mosaic—a vibrant and constantly updating picture of the person’s life.”   Leon relied on the D.C. Circuit’s prior decision in United States v. Maynard, which had developed what Orin Kerr has described as the mosaic theory of the Fourth Amendment.  In Maynard, the D.C. Circuit explained that long-term surveillance via installation of a GPS device in a car, which the government monitored for nearly a month as one of the defendants drove it, enabled the government to gather sufficient information about the defendant that it could eventually obtain a full picture of his life.

Reviewing the D.C. Circuit’s Maynard decision in United States v. Jones, the Supreme Court agreed that installation of the GPS device constituted a search under the Fourth Amendment.  Although the five-Justice majority employed a traditional Fourth Amendment analysis that focused on the physical intrusion associated with installation of the GPS device, concurring opinions by Justices Alito and Sotomayor expressed support for some version of a mosaic approach, which considered the length of monitoring and the amount and nature of information gathered.

The mosaic theory is a fundamental principle of intelligence gathering.  As David Pozen has explained, “[d]isparate pieces of information, though individually of limited or no utility to their possessor, can take on added significance where combined with other items of information.”  The theory’s most familiar use has been in the classification of documents and withholding of documents sought under the Freedom of Information Act (FOIA).  The government has invoked the theory with increasing frequency since 9/11 in resisting FOIA requests perceived to implicate national security, leading to what Jameel Jaffer has described as “a concentration of information in government hands.”  In Center for National Security Studies v. U.S. Department of Justice, for example, the D.C. Circuit applied the mosaic theory to justify the Justice Department’s refusal to provide information about hundreds of individuals swept up and detained following the 9/11 attacks.  The Third Circuit similarly relied on the theory in North Jersey Media Group v. Ashcroft in upholding the government’s decision to close to the press and public immigration court hearings involving post-9/11 detainees.  The information provided at public hearings, the Third Circuit reasoned, “could allow terrorist organizations to alter their patterns of activity to find the most effective means of evading detection,” while information that was not presented at the hearings could “provide important clues to terrorists, because it could reveal what the investigation has not yet discovered.”   

The mosaic theory’s translation from FOIA to the Fourth Amendment is not without obstacles.  Professor Kerr, for example, questions how a court should determine when a mosaic has been created within the meaning of the Fourth Amendment.  Yet, merely because such line-drawing poses challenges does not mean courts should not engage in it to determine what expectations about monitoring are reasonable.   Ultimately, a mosaic approach, which looks critically at the quantity and quality of information obtained, offers a way to make the Fourth Amendment relevant to the reality of big data and the potentially significant privacy intrusions accompanying it.

In the FOIA context, the mosaic theory provides a means for the government to maintain control over the increasing amount of information generated and gathered, even at the cost of denying the public access.  Incorporating a mosaic approach under the Fourth Amendment would extend the same rationale—that aggregating seemingly isolated data points can reveal a composite much greater than the sum of its parts—to the protection of individual privacy interests.  Put another way, if the FOIA-based mosaic rationale is correct, the government’s bulk collection of metadata raises important privacy concerns relevant to the Fourth Amendment.