When I was first introduced to the constitutional regulation of criminal procedure in the mid-1950s, a single issue dominated the field: To what extent did the due process clause of the Fourteenth Amendment impose upon states the same constitutional restraints that the Fourth, Fifth, Sixth and Eighth Amendments imposed upon the federal government? While those Bill of Rights provisions, as even then construed, imposed a broad range of constitutional restraints upon the federal criminal justice system, the federal system was (and still is) minuscule as compared to the combined systems of the fifty states. With the Bill of Rights provisions having long been held to apply only to the federal government, the Fourteenth Amendment's due process clause, because it did apply to the states, was the key to providing federal constitutional regulation of the vast bulk of law enforcement activities and criminal proceedings. The Supreme Court had repeatedly held that the Fourteenth Amendment's due process clause had a content that was independent of the Bill of Rights. That clause demanded "fundamental fairness," which could overlap in part with the protections found in the Fourth, Fifth, Sixth and Eighth Amendments, but was much narrower in scope. During the 1950s, as it had for the previous several decades, the Court pursued, on a case-by-case basis, the task of answering the question of precisely how far that overlap did extend.
Israel, Jerold H. "Free-standing Due Process and Criminal Procedure: The Supreme Court's Search for Interpretive Guidelines." St. Louis U. L. J. 45, no. 2 (2001): 303-432.