In McNabb v. United States, the Supreme Court claimed- for the first time in its history-the prerogative of "establishing and maintaining civilized standards of procedure and evidence" in the exercise of "supervisory authority over the administration of criminal justice in the federal courts." Since then, the Court has used this self-declared oversight power on numerous occasions and for a wide variety of purposes, but it has never adequately explained either the provenance or the scope of this type of judicial authority. Lower federal courts have followed suit, on the largely unexamined assumption that they too are endowed with supervisory authority, and have employed that power even more freely than has the Supreme Court.
From the perspective of the executive branch, the most critical aspect of supervisory power has been its use by the judiciary to adopt exclusionary rules of evidence and to recognize defenses unknown to the common law in an effort to deter misconduct on the part of federal investigators. The use of supervisory power by the judicial branch to control law enforcement activities by the executive branch is troubling for several reasons, not the least of which is that there appears to be no sound constitutional or other legal basis for this practice. As a result, such uses of supervisory power violate the fundamental principle of separation of powers. They also disregard the will of Congress and ultimately frustrate the search for truth in criminal investigations and prosecutions.
Department of Justice Office of Legal Policy,
The Judiciary's Use of Supervisory Power to Control Federal Law Enforcement Activity,
U. Mich. J. L. Reform
Available at: https://repository.law.umich.edu/mjlr/vol22/iss3/9