The exclusionary rule provides that evidence seized illegally in violation of the Bill of Rights cannot be used to convict a person of a crime. The exclusionary rule operates as a judicially created remedy designed to safeguard against future violations of Fourth Amendment rights through the rule’s general deterrent effect. Justice Benjamin Cardozo famously described it when he was a New York state court judge in 1926 as “the criminal goes free because the constable has blundered.”

The Rehnquist Court expanded the reach of the exclusionary rule, continuing a trend that developed during the Burger Court. In Illinois v. Krull (1987), the Court ruled that the exclusionary rule did not apply when a law enforcement official relied on a state statute that authorized warrantless searches even though the statute was subsequently declared unconstitutional. “Unless a statute is clearly unconstitutional, an officer cannot be expected to question the judgment of the legislature that passed the law,” Justice Harry Blackmun wrote for the Court. “If the statute is subsequently declared unconstitutional, excluding evidence obtained pursuant to it prior to such a judicial declaration will not deter future Fourth Amendment violations by an officer who has simply fulfilled his responsibility to enforce the statute as written.” In Arizona v. Evans (1995), the Court ruled 6–3 that the exclusionary rule did not prohibit the introduction of evidence seized from a person after an arrest that was based on a computer error. The Court held that evidence seized in violation of the Fourth Amendment as a result of clerical errors of court employees, causing incorrect computer records, fell within the Leon good faith exception to exclusionary rule. The Court noted that “the exclusionary rule was historically designed as a means of deterring police misconduct, not mistakes by court employees.”