How does the exclusionary rule limit the use of evidence seized in violation of the Fourth Amendment?

The exclusionary rule is a legal principle in the United States that prohibits the use of evidence obtained by police in violation of a defendant's Fourth Amendment rights against them during a criminal trial.12

By mandating the exclusion of such evidence, the rule serves as a critical safeguard for the constitutional right to be secure against unreasonable searches and seizures. While the rule was initially applied only in federal courts, the U.S. Supreme Court extended its application to all state and federal criminal proceedings in the landmark case Mapp v. Ohio (1961).132

However, the rule is not absolute. Legal exceptions have been established, most notably the "good faith" exception. As held in U.S. v. Leon (1984), evidence obtained by officers acting in good faith—such as relying on a search warrant that is later determined to be invalid—may still be admissible in court. This reflects a judicial balance between protecting individual privacy and the social costs of excluding potentially relevant evidence.1