Mapp v. Ohio (1961) is the first of a series of cases in which the Warren Court incorporated various procedural aspects of the Bill of Rights to make them fully applicable against the states by the Due Process Clause of the Fourteenth Amendment. In Mapp, Cleveland police officers had entered Dollree Mapp’s home on the suspicion that a suspect in a recent bombing was taking refuge there. They did not have a search warrant. The police did not find the suspect that they were looking for, but did find several books and magazines that were obscene under Ohio law. Mapp appealed her conviction for possession of obscene materials by claiming that without a warrant, the materials taken from her home were seized in violation of the Fourth and Fourteenth Amendments of the Constitution and therefore inadmissible in court.
In Wolf v. Colorado (1949), the Court had held that while the Fourth Amendment’s guarantee against unreasonable searches and seizures was incorporated by the Due Process Clause of the Fourteenth Amendment, the exclusionary rule was not. The Mapp decision overturned Wolf and made the exclusionary rule part and parcel of the Fourth Amendment and therefore incorporated against the states by the Due Process Clause of the Fourteenth Amendment.
Later decisions by the Supreme Court have made exceptions to the exclusionary rule without ever overturning it. For example, in United States v. Calandra (1974), the Court held that while evidence obtained without a search warrant was not admissible in trial, it could be introduced to a grand jury that was determining whether to indict the suspect. In United States v. Leon (1984), the Court held that if the police obtain a warrant that later is found to be invalid, the evidence is still admissible during the trial. And in Pennsylvania Board of Probation v. Scott (1998), the Supreme Court decided that illegally seized evidence could be introduced during parole revocation hearings. These decisions have left the main thrust of the original Mapp decision intact, but have narrowed when and where the exclusionary rule is applicable.
Mapp v. Ohio 367 U.S. 643 (1961); and Potter Stewart, “The Road to Mapp v. Ohio and Beyond: The Origins, Development and Future of the Exclusionary Rule in Search-and Seizure Cases,” Columbia Law Review 83 (1983): 1365.