Chicago Police Department (CPD) Practice Exam 2026 - Free CPD Practice Questions and Study Guide

The case that established the exclusionary rule for state courts is Mapp v. Ohio. This landmark decision in 1961 extended the exclusionary rule, which prohibits the use of illegally obtained evidence in federal courts, to state courts through the Fourteenth Amendment's Due Process Clause. Prior to this case, the exclusionary rule was primarily applied at the federal level, but Mapp v. Ohio ensured that states also had to adhere to this principle, reinforcing the protection of individual rights against unlawful searches and seizures. This ruling has had a significant impact on law enforcement practices across the United States, emphasizing the need for lawful procedures in gathering evidence.