Mapp v. Ohio (1961) was a landmark United States Supreme Court case regarding the Fourth Amendment of the United States Constitution as it relates to criminal procedure. The Court held that evidence that was obtained in violation of the Fourth Amendment could not be used against someone in State or Federal court.
The Fourth Amendment protects the rights of people from "unreasonable searches and seizures", as well as ensures that no warrants are issued without probable cause. Mapp v. Ohio was the first time this Amendment was applied to criminal procedure in State courts.
A Cleveland, Ohio woman, Dollree Mapp, was suspected of harboring a fugitive in her home. Police officers arrived at her home and demanded entrance. When she refused, they forcibly broke down her door and entered the premises. Mapp requested a search warrant from the officers who presented a piece of paper they claimed was a valid search warrant, but did not allow her to view it. Upon searching the entire house, the officers did not find a fugitive. Instead they discovered a trunk containing lewd photographs and books.
Mapp was arrested based on the violation of an Ohio law banning obscene material. The evidence discovered by police in her home was presented and used against her in court. In Mapp v. Ohio, the police officers never actually presented a search warrant to the court. Mapp was convicted and appealed this decision to the Supreme Court of the United States.
Although two previous Supreme Court cases regarding criminal procedure had found that evidence obtained illegally could not be used against the defendant in court, this had never been applied in State courts before Mapp v. Ohio. It was not until this landmark case that this exclusionary rule began to be enforced in criminal procedure. This case was decided on a 6-3 vote.
In the majority opinion written by Justice Thomas Clark, the Court held that the exclusionary rule also applies to State courts. The Court used the rights of the Fourth Amendment that protect against unreasonable searches, as well as the Due Process Clause of the Fourteenth Amendment. This Clause protects citizens from the loss of liberties without due process of the law.
Justice Clark added to the decision by saying that it does not in any way permit criminals to break the law simply because of the police officer's error in criminal procedure. He observed that the exclusionary rule is imminent in both these Amendments and that the Government must abide by its own laws.
Another concurring Justice wrote that this decision of the Court was also based on the Fifth Amendment of the Constitution. The Fourth Amendment's protection against unreasonable search and seizure, he claimed, was not binding enough to deny the use of illegally obtained evidence from being used to convict a criminal. However, in combination with the Fifth Amendment, which protects against self-incrimination, the use of this evidence in criminal procedure is unconstitutional. Mapp v. Ohio was influential in providing stricter enforcement of the exclusionary rules, as well as extending this policy to use in State courts.