Search, seizure and false (?) arrest: an analysis of fourth amendment remedies when police can plant evidence

Abstract

The Fourth Amendment prohibits unreasonable searches and seizures in criminal investigations. The Supreme Court has interpreted this to require that police obtain a warrant prior to search and that illegally seized evidence be excluded from trial. A consensus has developed in the law and economics literature that tort liability for police officers is a superior means of deterring unreasonable searches. We argue that this conclusion depends on the assumption of truth-seeking police, and develop a game-theoretic model to compare the two remedies when some police officers (the “bad” type) are willing to plant evidence in order to obtain convictions, even though other police (the “good” type) are not (where this type is private information). We characterize the perfect Bayesian equilibria of the asymmetric-information game between the police and a court that seeks to minimize error costs in deciding whether to convict or acquit suspects. In this framework, we show that the exclusionary rule with a warrant requirement leads to superior outcomes (relative to tort liability) in terms of truth-finding function of courts, because the warrant requirement can reduce the scope for “bad” types of police to plant evidence. Acknowledgments: We would like to thank Tue Gorgens and Eli Wald for helpful discussions, and seminar participants at the University of Connecticut for valuable comments. 1) Introduction The prosecution of criminal defendants is a process fraught with uncertainty, and requires a delicate balance between the search for the truth, and the protection of citizens’ right to be free from unreasonable invasions of their privacy. An important legal safeguard in this context is the Fourth Amendment to the U.S. Constitution, which provides that “The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no warrants shall issue, but upon probable cause...” (U.S. Const., Amendment IV). The Supreme Court has interpreted this amendment to require that police, when feasible, obtain a warrant prior to search, which a judge will only issue on a finding of probable cause (the “warrant requirement”), and further, that any illegally obtained evidence will be excluded from trial (the “exclusionary rule”). Scholars have vigorously debated the desirability of these remedies for violations of the Fourth Amendment. A major focus of the debate has been on the relative merits of the warrant requirement and exclusionary rule on the one hand, and a reasonableness standard enforced by tort liability for the government or its agents on the other. Amar (1997, Chapter 1), for example, argues that the plain language of the Fourth Amendment does not require warrants, probable cause, or exclusion of evidence, but only that searches and seizures be reasonable. Further, the courts, in recognizing the impracticality of the warrant requirement in many contexts, have historically granted many exceptions to it (for example, use of metal detectors in airports). Finally, Amar claims on historical grounds that the Framers themselves envisioned tort liability (in the form of a civil action for trespass) rather than exclusion as the principal remedy for unlawful seizures of evidence. Posner (1981) has also argued for replacement of the exclusionary rule with tort liability, based however on economic rather than textual or historical considerations. As noted above, the primary objective of rules against unreasonable search is to balance citizens’ right to privacy against the goal of truth-seeking in criminal proceedings. Given this trade-off, economic efficiency requires that searches should be allowed up to the point where the expected probative value of the evidence being sought equals the harm to the victim of the search. Under such a 1 See, for example, Weeks v. United States, 232 U.S. 383n (1914); and Mapp v. Ohio, 367 U.S. 643 (1961), which extended these provisions to the states. 2 Formally, if B is the harm to the victim in terms of impaired privacy, p is the probability that evidence will be discovered that is decisive for conviction, and L is the social loss of not convicting the defendant, then a search is