Mapp v. Ohio, case decided in 1961 by the U.S. Supreme Court. Dollree Mapp was convicted in a state court of possessing pornographic material in violation of Ohio law. Her conviction was obtained on the basis of evidence taken by the police when they entered (1957) her boardinghouse without a search warrant while looking for gambling materials. The Supreme Court, in overturning her conviction, declared that the exclusionary rule (based on the Fourth Amendment to the Constitution), which prohibits the use in federal court of evidence obtained through an illegal search and seizure, extended also to state courts. The ruling provoked a good deal of controversy; while proponents of the exclusionary rule claim that it is the only means of assuring freedom from illegal searches, opponents argue that a criminal should not go free because of a police officer's violation of the Constitution.