The Supreme Court ruled that the Fourth Amendment did not prohibit the admission of criminal evidence obtained from a search conducted pursuant to a warrant issued by a neutral and detached magistrate even if the warrant was ultimately found invalid through no fault of the police officers conducting the search.

Based on an affidavit referring to a confidential informant and various police observations, a state judge issued a search warrant authorizing police officers to search the residences of Alberto Leon and two other suspects. In the ensuing search, the police found large quantities of illegal drugs. At the trial, however, the court determined that the affidavit was insufficient to establish probable cause, and the evidence was thrown out.Good faith exception;Leon, United States v.[Leon, United States v.]

By a 6-3 vote, the Supreme Court adopted the good faith exception, which stipulated that the exclusionary rule would not apply when the police were acting from an “objectively reasonable” belief that a search warrant is valid, even if the warrant later proves to be defective. Justice Byron R. White’sWhite, Byron R.;Leon, United States v.[Leon, United States v.] majority opinion warned of the social costs of excessive interference with the criminal justice system’s “truth-finding function,” and he insisted that the exclusionary rule was designed only as a deterrent to police misconduct, not to prevent judicial errors. In dissent, Justice William J. Brennan, Jr., argued that the Fourth Amendment requires the suppression of unconstitutionally seized evidence without any regard to its deterrent effect.

Although the Leon ruling was rather narrow, the Court subsequently extended the conditions for applying the good faith exception to the exclusionary rule. In Illinois v. Krull[case]Illinois v. Krull[Illinois v. Krull] (1987), a 5-4 majority of the justices upheld the admission of evidence obtained in a warrantless search authorized by a statute that was later found unconstitutional. In Arizona v. Evans[case]Arizona v. Evans[Arizona v. Evans] (1995), a 7-2 majority allowed the use of evidence found in a search resulting from police reliance on mistaken court records of outstanding arrest warrants.

Exclusionary rule

Fourth Amendment

Mapp v. Ohio

Search warrant requirement