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Stanford Law Review

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The exclusionary evidence rules derived from the Fourth, Fifth, and Sixth Amendments continue to play an important role in constitutional criminal procedure, despite the intense controversy that surrounds them. The primary justification for these rules has shifted from an "imperative of judicial integrity" to the "deterrence of police conduct that violates... [constitutional] rights." Regardless of the justification it uses for the rules' existence, the Supreme Court continues to limit their breadth "at the margin," when "the acknowledged costs to other values vital to a rational system of criminal justice" outweigh the deterrent effects of exclusion. The most notable limitation on the exclusionary rules is the impeachment exception, which permits the use of illegally obtained evidence at trial to impeach the defendant's testimony. The shift from a judicial integrity rationale to a deterrence rationale for the rules, however, does not explain the origins of this exception. The Court created the impeachment exception in 1954 in Walder v. United States before rejecting the judicial integrity approach. Walder suggests that the Court has supported the exception based on principle, as well as on policy considerations. This article argues that attempts to justify the impeachment exception as a matter of policy or as a matter of principle are equally misguided. Both methods wrongly consider the integrity of factfinding at a criminal trial a value that can meaningfully be balanced against the constitutional values protected by the exclusionary rules.Instead, a coherent approach to the scope of the exclusionary rules must approach that question entirely as a matter of constitutional criminal procedure. Constitutional guarantees do not supply independent values to balance against the integrity of factfinding-they define that integrity. Consequently, the impeachment exception should be eliminated because it improperly compromises constitutional rules of criminal procedure in the name of furthering what the Court claims to be "other values vital to a rational system of criminal justice."