Which case established the exclusionary rule prohibiting the use of illegally obtained evidence in state courts?

• A. Mapp v. Ohio (1961)
• B. Gideon v. Wainwright (1963)
• C. United States v. Lopez (1995)
• D. Heart of Atlanta Motel v. United States (1964)

Answer: (A)

Extending the exclusionary rule to state courts through incorporation of the Fourth Amendment. The idea is that protections against unreasonable searches and seizures apply to state actors as well as the federal government. Previously, the exclusionary rule had limited reach to federal prosecutions, with Wolf v. Colorado allowing states to choose whether to apply it. Mapp v. Ohio held that evidence obtained in violation of the Fourth Amendment cannot be used in state criminal prosecutions, applying the rule to the states via the Fourteenth Amendment’s due process clause. This decision made the exclusionary rule a binding principle in state courts, preventing illegally obtained evidence from being used at trial. In practice, it addressed a situation where unlawful searches led to convictions, and the Court reversed those outcomes to uphold Fourth Amendment protections.

For context, the ruling relies on incorporation—that fundamental rights protected against the federal government are also protections against state actions. The case involved a police search without proper warrant procedures and the discovery of incriminating material, which led to suppression of the evidence and a reversal of the conviction at the state level.

Other choices concern different constitutional issues: one focuses on right to counsel, another on limits of Congress’s power, and another on civil rights under the Commerce Clause. None of these establish the rule that illegally obtained evidence cannot be used in state courts.