Dirty Hands or Deterrence? An Experimental Examination of the Exclusionary Rule

Abstract

Historically, the Supreme Court has offered two justifications for the Exclusionary Rule: one, it protects the integrity of the judicial system from “dirty” evidence, and two, it deters illegal searches by the police. The former justification has mostly fallen out of favor. Today, decisions turn on whether the Rule would, in fact, deter illegal searches in a given class of cases. As such, most empirical studies about the Rule have focused on whether or not the Rule leads to fewer police searches (illegal or otherwise), or to fewer criminal convictions.

This study takes a completely different approach, assessing support for the two competing justifications for the Rule. Two experiments show support for the integrity justification for the Rule, but not for the deterrence justification. Specifically, when deciding whether to exclude evidence found during a search conducted without probable cause, participants are sensitive to a police officer’s motive (clean vs. dirty), but not to alternative means of punishing those officers (civil suit, citizen-police review board). A third experiment examines the integrity rationale in more detail. Participants who were obligated to use dirty evidence at trial disproportionately selected a bottle of Purell over a pen as a thank you gift, versus participants who were able to exclude that evidence. In other words, the Exclusionary Rule seems to protect the courts from being metaphorically tainted.

These findings are important given that the Rule is not constitutionally mandated. The Supreme Court has held that the Rule can be ignored to the extent that it (a) does not achieve its goals and (b) undermines the perceived legitimacy of the courts by the public. Given this, the Court needs to be right about what those goals are, and whether or not its current deterrence-based jurisprudence enhances legitimacy. These experiments suggest the possibility that reinvigorating the integrity justification would serve the ends of the Rule better than current doctrine does.

Keywords: Exclusionary Rule, expressive, consequentialist, symbolic, deterrence, evidence, Whren, Driving While Black, Fourth Amendment