motion or on the request of a participant in a court proceeding. In cases

involving the victims of crimes, confidential informants, undercover agents and in evidentiary suppression hearings, a presumption of validity attends such requests. The trial judge shall exercise broad discretion in deciding whether there is cause for prohibition. This list of requests which enjoy the presumption of validity is not exclusive; the court may, in its discretion, find cause for prohibition in comparable situations. Compare. — Rule 53, Fed. Rules Cr. Proc.