Which case extended the exclusionary rule to the states, reinforcing due process protections?

• A. Miranda v. Arizona (1966)
• B. Gideon v. Wainwright (1963)
• C. In re Gault (1967)
• D. Mapp v. Ohio (1961)

Answer: (D)

The key idea is applying protections against unlawful searches and seizures to state courts through incorporation of the Fourth Amendment via the Fourteenth Amendment. Mapp v. Ohio held that evidence obtained in violation of the Fourth Amendment cannot be used in state prosecutions, making the exclusionary rule binding on the states. This reinforces due process by ensuring that illegal police conduct cannot lead to conviction, no matter where the case is tried. The decision rests on the incorporation doctrine, which extends Bill of Rights protections to state actions through the Fourteenth Amendment. Before this, the exclusionary rule mainly constrained federal investigations. The other options address different rights: warnings during custodial interrogation, right to counsel, and juvenile due process, none of which involve extending the exclusionary rule to the states.