Exclusionary rule applied to state prosecutions. Decided June 18, 1961 (argued March 29, 1961). Opinion of the Court: Thomas Campbell Clark → go there Dissenting: Harlan. Applied: the Fourth Amendment → go there Applied: the Fourteenth Amendment → go there Topic: Fourth Amendment rights. Mapp v. Ohio, 367 U.S. 643 (1961), is a landmark U.S. Supreme Court decision in which the Court ruled that the exclusionary rule, which prevents a prosecutor from using evidence that was obtained by violating the Fourth Amendment to the U.S. Constitution, also applies to the states. Wiki link