Can a prosecuting attorney be disqualified as a witness?

When a prosecuting attorney is a witness to a crime, the true danger lies not in his having witnessed the event, but in his performing the dual role of prosecutor and witness. If he is to prosecute the case, and also to testify as a prosecution witness, he should be disqualified. It would be impossible for him to be a part of the evidence and, at the same time, to present that evidence impartially as is his bounden duty. (See, Berger v. United States (1935) 295 U.S. 78, 88, 55 S.Ct. 629, 633, 79 L.Ed. 1314.)