All law students study Mapp v. Ohio (1961). In this landmark case, the Supreme Court held that the exclusionary rule should be applied to state criminal prosecutions. In other words, evidence seized in violation of the Fourth Amendment could not be admitted in Court. Previously, in Wolf v. Colorado (1949), the Supreme Court declined to "incorporate" the exclusionary rule. (Incorporation is not exactly the right term here, but it is close enough.) Rather, Wolf held, the exclusionary rule would only be enforced with regard to federal criminal prosecutions as part of the Supreme Court's "supervisory power" of the lower courts.
In the lower courts, Mapp was litigated as a First Amendment case. Dollree Map was arrested for possessing certain obscene materials. Indeed, the oral arguments focused extensively on the First Amendment issues. It was not litigated as a Fourth Amendment case.
Mapp's counsel did not ask the Supreme Court to overrule Wolf. Justice Frankfurter pointed out that the counsel for Mapp did not even mention Wolf in their brief.
