A Hard Look at What We Know (and Still Need to Learn) About the "Costs" of the Exclusionary Rule: The NIJ Study and Other Studies of "Lost" Arrests

The controversy over a "good faith mistake" exception to the exclusionary rule and the 1982 National Institute of Justice study of the effects of the rule in California have focused attention on the "costs" of the rule. This article reviews the NIJ study and seven other relevant studies and concludes that the NIJ study's claim that the rule has a "major impact" on the disposition of felony arrests is misleading and exaggerated. California data show that prosecutors reject only 0.8% (8 in 1,000) of felony arrests because of illegal searches. The effect of the rule is concentrated in drug cases in which the rejection rate by prosecutors is 2.4% (not 30%, as suggested by the NIJ study), but the rejection rate for non-drug arrests is less than 0.3%, and the rate is even lower for violent crimes. Even if one looks at the cumulative effect of the rule through all stages of the felony process in California, only about 2.35% of felony arrests are lost because of illegal searches, and this is a high-side estimate based on potentially atypical samples. Moreover, studies of "lost arrests" have not differentiated between arrests resulting from bona fide crime investigations and arrests that resulted from arbitrary searches or arrests that were made to seize contraband, for harassment, or for purposes other than obtaining a conviction. The author concludes that available data show the cost of the rule is marginal, especially in view of the ambiguous nature of the lost arrests. Moreover, it is doubtful that a good faith mistake exception would save any substantial proportion of the arrests lost following illegal searches. In particular, an exception for searches conducted under an improper warrant would save only a negligible proportion of lost arrests.