Mapp v. Ohio

367 U.S. 643 (1961), established that illegally obtained evidence cannot be produced at trial in a state court to substantiate criminal charges against the defendant. The Court relied on the earlier decision in Weeks v. United States, 222 U.S. 383 (1914). Weeks established the exclusionary rule, which states that a person whose Fourth Amendment protections against unreasonable search and seizure have been violated has a right to exclude any evidence so obtained from use in a court of law. In Mapp the Court held that the exclusionary rule had to be applied universally to all criminal proceedings, overturning the ruling in Wolf v. Colorado, 338 U.S. 25 (1949), insofar as it failed to hold the exclusionary rule applicable to state court proceedings, and thus greatly broadening the constitutional protections available to defendants. In United States v. Leon, 468 U.S. 897 (1984), the court validated an exception to the exclusionary rule, holding that evidence which is obtained “in good faith” with a search warrant that is later ruled invalid remains admissible, a central point made in support of the decision being the unacceptable social cost of excluding such evidence.