In which case did the Supreme Court establish that illegally obtained evidence cannot be used in court?

The Supreme Court case that established the principle that illegally obtained evidence cannot be used in court is Mapp v. Ohio. This landmark decision extended the exclusionary rule, which prevents the admission of evidence obtained through violations of the Fourth Amendment (protection against unreasonable searches and seizures), to state courts. Prior to this case, the exclusionary rule was primarily applied only in federal courts.

The ruling stemmed from a situation in which police unlawfully searched the home of Dollree Mapp without a proper warrant and found illegal materials. The Court held that the evidence obtained from this unlawful search was inadmissible in court, thus reinforcing the notion that constitutional rights must be upheld and that a violation of those rights brings serious consequences in legal proceedings. This case set a critical precedent in American law regarding the handling of evidence and the protection of individual rights within the judicial system.