What is the role of a district judge in protecting the rights of a criminal defendant?

We emphatically reject this argument. "The task of safeguarding the rights of criminal defendants ultimately rests with the experienced men and women who preside in our district courts." United States v. Balough, 820 F.2d 1485, 1491 (9th Cir.1987). That a district judge's responsibility does not end when he rules on objections and motions raised by the parties is recognized by the doctrine of plain error, which embodies the notion that there are some errors that are so prejudicial and obvious the district judges must remedy them even without an objection. ¹

Where a district judge detects what he suspects may be an error seriously affecting the rights of a criminal defendant, he must address the problem. This duty exists at all times, but never more so than when the problem is such that it is unlikely to be detected by an individual defendant. The matter that gave the district judge pause here--his suspicion that the United States Attorney was engaging in unconstitutionally selective prosecution--can rarely be identified based on a single case. A district judge who perceives a pattern of invidious enforcement has ample authority under the court's supervisory powers to raise the matter sua sponte. See United States v. Simpson, 927 F.2d 1088, 1090-91 (9th Cir.1991). While we disapprove of the manner in which the district judge handled the issue after he identified the problem, see pages 1302-03 infra, we commend his alertness and initiative in addressing a practice he had reason to believe impaired the fundamental fairness of the proceedings before him.