The Warren Court left an unprecedented legacy of judicial activism in the area of civil rights law as well as in the area of civil liberties—specifically, the rights of the accused as addressed in Amendments 4 through 8. In the period from 1961 to 1969, the Warren Court examined almost every aspect of the criminal justice system in the United States, using the 14th Amendment to extend constitutional protections to all courts in every State. This process became known as the “nationalization” of the Bill of Rights. During those years, cases concerning the right to legal counsel, confessions, searches, and the treatment of juvenile criminals all appeared on the Court's docket.
The Warren Court's began with the case of Mapp v. Ohio, which was the first of several significant cases that re-evaluated the role of the 14th Amendment as it applied to state judicial systems.
In a 6-3 decision, the Court overturne the conviction, and five justices found that the States were bound to exclude evidence seized in violation of the 4th Amendment. The 4th Amendment sets the standards for searches and seizures by law enforcement officials in the United States, the Court noted, and the 14th Amendment requires judges to uphold those standards in every State.
Evidence gained by an illegal search became inadmissible in State courts as a result of the decision. The “Mapp Rule” has since been modified, so the exclusionary rule is no longer as absolute as when first handed down in Mapp. Critics of the Warren Court charged that it “had gone too far in interfering with police work.”
With its decisions in the cases of Mapp v. Ohio, Gideon v. Wainwright, and Escobedo v. Illinois the Warren Court handed down the bases of what it called the “fundamentals of fairness” standard. At both the State and federal level, the Court sent a clear signal to law enforcement and criminal justice officials.