On the role of the exclusionary rule for optimal law enforcement effort

• Author: Tim Friehe,Thomas J. Miceli
• Published date: 01 October 2018
• DOI: http://doi.org/10.1111/jpet.12321
• Date: 01 October 2018

757

Journal of Public Economic Theory. 2018;20:757–767. wileyonlinelibrary.com/journal/jpet © 2018 Wiley Periodicals, Inc.

Received: 18 April 2018 Accepted:21 May 2018

DOI: 10.1111/jpet.12321

ARTICLE

On the role of the exclusionary rule for optimal law

enforcement effort

Tim Friehe1,2,3 Thomas J. Miceli4

1Universityof Marburg, Marburg, Germany

2CESifo,Munich, Germany

3EconomiX,Paris, France

4Departmentof Economics, University of Con-

necticut,Storrs, CT

Correspondence

TimFriehe, University of Marburg, Am Plan 2,

35037Marburg, Germany.

Email:tim.friehe@uni-marburg.de.

This article explores the role of the exclusionary rule for improving

the level of law enforcement. In a setup in which the enforcement

authority and the offender choose effort levels in a struggle to influ-

encethe probability of detection, exclusionof excessive evidence can

be welfare-improving because it allows the social planner to commit

to low enforcement effort.

1INTRODUCTION

The Fourth Amendment to the U.S. Constitution forbids unreasonable searches and seizures in connection with crim-

inal investigations. This has been interpreted by the Supreme Court to require that, when feasible, police must obtain

a warrant prior to search, which would only be issued by a court conditional on the police showing probable cause that

a crime has been committed. Further,any evidence obtained without a warrant (with some few exceptions) would be

excluded from use in a trial of the defendant. This is referred to as the “exclusionary rule.” The claimed purpose of the

rule is to protect the privacy rights of citizens, but it is controversial because it is often seen as protecting the rights

of guilty defendants. A simple cost–benefit analysis shows that the rule can indeed result in excessive exclusion of

evidence.1

This article examines the effect of the exclusionary rule on optimal law enforcement. It builds upon the model of

Friehe and Miceli (2017), which examinesthe strategic interaction between potential offenders and the enforcement

authority. Specifically,offenders choose whether or not to engage in criminal activity, and conditional on a decision

to become a criminal, how much effort to devote to avoiding capture.2The enforcement authority simultaneously

chooses how much effort to invest in apprehension (which in the current context we will interpret to be evidencecol-

lection). The Nash equilibrium determines the conviction rate,and hence the level of crime. We allow the objectives of

the enforcement authority to divergefrom society's, however, by assuming that they ignore the benefits of crime to the

offenders.3For example, Baickerand Jacobsen (2007) present evidence on the fundamental disconnect between the

1Tosee why, let Bbe the social cost of a search in terms of the impaired privacy rights of the target, Pthe probability that critical evidence will be found by

thesearch, and Lthe social benefit of conviction (including the deterrence benefits). The search is therefore beneficial if B<PL. However, an exclusionary rule

thatrequires P≥

Pforsome threshold 

Pforthe search to be “legal” would exclude those beneficial searches for which 

P>P>B∕L.This could be true if, say, B

is small and/orLis large. In recognition of this problem, Posner (1981) has suggested replacing the exclusionary rule with tort liability for police who conduct

illegalsearches. The logic is that the threat of liability will efficiently deter wrongful police behavior but without benefiting criminals.

2Malik (1990) introduced avoidance into the literature on optimal law enforcement. Later important contributions include Dechenaux and Samuel (2016),

Langlais(2008), Nussim and Tabbach (2008, 2009), Sanchirico (2006), and Tabbach(2010).

3Incorporatingprivacy costs would only reinforce this tendency, as we argue in Section 4.