In Campbell v. United States, 365 U.S. 85, 81 S.Ct. 421, 5 L.Ed.2d 428 (1961), the Supreme Court noted that where the agent who authored the "interview report" at the center of a Jencks Act inquiry was available to testify regarding whether "the report was a contemporaneously recorded substantially verbatim recital of a witness' oral statement", then "the circumstances of this case clearly required that the judge call this agent of his own motion or require the Government to produce him." Id. at 426-427