The mosaic theory of the Fourth Amendment.

• Author: Kerr, Orin S.

In the Supreme Court's recent decision on GPS surveillance, United States v. Jones, five justices authored or joined concurring opinions that applied a new approach to interpreting Fourth Amendment protection. Before Jones, Fourth Amendment decisions had always evaluated each step of an investigation individually. Jones introduced what we might call a "'mosaic theory'" of the Fourth Amendment, by which courts evaluate a collective sequence of government activity as an aggregated whole to consider whether the sequence amounts to a search.

This Article considers the implications of a mosaic theory of the Fourth Amendment. It explores the choices and puzzles that a mosaic theory would raise, and it analyzes the merits of the proposed new method of Fourth Amendment analysis. The Article makes three major points. First, the mosaic them?' represents a dramatic departure from the basic building block of existing Fourth Amendment doctrine. Second, adopting the mosaic theory, would require courts to answer a long list of novel and challenging questions. Third, courts should reject the theory and retain the traditional sequential approach to Fourth Amendment analysis. The mosaic approach reflects legitimate concerns, but implementing it would be exceedingly difficult in light of rapid technological change. Courts can better respond to the concerns animating the mosaic" theory within the traditional parameters of the sequential approach to Fourth Amendment analysis.

TABLE OF CONTENTS INTRODUCTION I. THE SEQUENTIAL APPROACH TO THE FOURTH AMENDMENT A. Sequential Analysis in Search and Seizure Law B. The Search Inquiry Under the Sequential Approach C. Constitutional Reasonableness Under the Sequential Approach D. Constitutional Remedies Under the Sequential Approach II. MAYNARD/JONES AND THE INTRODUCTION OF THE MOSAIC THEORY A. The Facts of Maynard/Jones B. The D.C. Circuit's Opinion the Maynard C. The Supreme Court's Opinions in Jones III. IMPLEMENTING THE MOSAIC THEORY A. Identifying the Standard 1. Expectations of What? 2. The Stages of Surveillance B. The Grouping Problem: Developing a Theory of Aggregation for the Mosaic Search 1. Duration and Scale 2. Which Surveillance Methods Count? 3. Grouping Across Practices, Officers, and Investigations C. The Constitutional Reasonableness of Mosaic Searches D. Remedies for Mosaic Searches 1. Does the Exclusionary Rule Apply? 2. Standing to Challenge Mosaic Searches 3. Fruit of the Poisonous Tree and Inevitable Discovery IV. THE CASE AGAINST THE MOSAIC THEORY A. The Mosaic Theory as Equilibrium-Adjustment B. The Case Against the Mosaic Theory 1. The Mosaic Theory Would Be Very Difficult to Administer 2. Probabilistic Approaches to the "Reasonable Expectation of Privacy" Test Are Ill Suited to Regulate Technological Surveillance 3. The Mosaic Theory Could Interfere with More Effective Statutory Protections C. The Mosaic Theory as a Halfway Measure and the Katz Example CONCLUSION INTRODUCTION

The Fourth Amendment prohibits unreasonable searches and seizures, (1) and the most challenging and important threshold question in interpreting the Fourth Amendment is what counts as a "search. " (2) Identifying Fourth Amendment searches traditionally has required analyzing police action sequentially. (3) If no individual step in a sequence counts as a search, then the Fourth Amendment is not triggered. No Fourth Amendment violation has occurred.

In United States v: Maynard, (4) the D.C. Circuit introduced a different approach, which could be called a "mosaic theory" of the Fourth Amendment. (5) Under the mosaic theory, searches can be analyzed as a collective sequence of steps rather than as individual steps. (6) 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] The D.C. Circuit applied that test in Maynard to GPS surveillance of a car. The court held that GPS surveillance of a car's location over twenty-eight days aggregates into so much surveillance that the collective sequence triggers Fourth Amendment protection. (8)

When the Supreme Court reviewed Maynard in United States v: Jones, (9) concurring opinions signed or joined by five of the justices endorsed some form of the D.C. Circuit's mosaic theory. (10) The majority opinion resolved the case without reaching the mosaic theory, and neither concurring opinion gave the issue extensive analysis. But Justice Alito's concurring opinion for four justices clearly echoed the basic reasoning of the D.C. Circuit in concluding that long-term GPS monitoring of a car counts as a search even though short-term monitoring does not. (11) Justice Sotomayor's separate concurrence also voiced support for the mosaic approach. (12)

The concurring opinions in Jones raise the intriguing possibility that a five-justice majority of the Supreme Court is ready to endorse a new mosaic theory of Fourth Amendment protection. That prospect invites lower courts to consider whether the mosaic theory is viable and if so, how it should be applied. A handful of courts have begun to do so in the short time since the Court handed down Jones, with mixed results so far. (13) Law enforcement is paying close attention as well. Soon after Jones, the General Counsel of the Federal Bureau of Investigation informed a law school audience that the mosaic opinions in Jones were causing significant turmoil inside the FBI. (14)

The mosaic opinions in Jones implicate fundamental questions about the future of Fourth Amendment law. What might a mosaic theory mean? What challenges does it entail? Should lower courts eagerly adopt such a method, or do its risks outweigh its benefits? And when the mosaic theory eventually works its way back up to the Supreme Court, should the Court embrace it as a valid theory or reject it as misguided?

This Article considers the consequences of possible judicial adoption of a mosaic theory. It maps out the possible futures of the mosaic theory, and it details how the theory raises questions that courts will need to answer. (15) It also evaluates the merits of the mosaic approach and considers whether judges should accept the invitation to adopt it.

The Article makes three points. First, the mosaic theory is a major departure from the traditional mode of Fourth Amendment analysis. The current structure of Fourth Amendment doctrine hinges on what I call a "sequential approach." The sequential approach takes a snapshot of each discrete step and assesses whether that discrete step at that discrete time constitutes a search. This analytical method forms the foundation of existing Fourth Amendment doctrine, ranging from the threshold question of what the Fourth Amendment regulates to considerations of constitutional reasonableness and remedies. By aggregating conduct rather than looking to discrete steps, the mosaic theory offers a fundamental challenge to current Fourth Amendment law.

Second, implementing the mosaic theory would require courts to answer an extensive list of difficult and novel questions. Severing the Fourth Amendment from the sequential approach would compel courts to start afresh with a new building block of Fourth Amendment analysis. For example, what is the standard for the mosaic? How should courts aggregate conduct to know when a sufficient mosaic has been created? Which techniques should fall within the mosaic approach? Should mosaic searches require a warrant? If so, how can mosaic warrants satisfy the particularity requirement? Should the exclusionary rule apply to violations of the mosaic search doctrine? Who has standing to challenge mosaic searches? Adopting a mosaic theory would require courts to answer all of these questions and more.

Third, as a normative matter, courts should reject the mosaic theory. The mosaic approach is animated by legitimate concerns: it aims to maintain the balance of Fourth Amendment protection as technology changes, a method I have elsewhere called "equilibrium-adjustment." (16) But it aims to achieve this reasonable goal in a peculiar way. By rejecting the building block of the sequential approach, the mosaic theory would be very difficult to administer coherently. Even if courts could develop answers to the many questions the theory raises, doing so would take many years--by which time the technologies regulated by the theory would become obsolete. The mosaic theory would also deter enactment of statutory privacy regulations and force judges to consider questions that they are poorly equipped to answer. If courts must broaden Fourth Amendment rules in response to new technologies, the better approach is to rule that certain steps are always searches. The model should be the Supreme Court's famous decision in Katz v. United States, (17) not the concurring opinions in Jones.

This Article proceeds in four parts. Part I introduces the sequential approach that forms the basis lot existing Fourth Amendment doctrine. Part II provides a close analysis of the D.C. Circuit and Supreme Court decisions on the mosaic theory in Maynard and Jones. Part III catalogs and considers the many difficult issues that courts would need to answer to implement the mosaic theory. Finally, Part 1V argues that courts should reject the mosaic theory and retain the traditional sequential approach to interpreting the Fourth Amendment.

1. THE SEQUENTIAL APPROACH TO THE FOURTH AMENDMENT

   This Section explains how the sequential approach to Fourth Amendment analysis forms the building block of modern Fourth Amendment doctrine. It begins by introducing the sequential approach and then examines the three basic stages of Fourth Amendment analysis: first, what is a search; second, when is a search unreasonable and therefore unconstitutional; and third, when does an unconstitutional search justify a remedy.

   1. Sequential Analysis in...