an issue at trial." United States v. Carson, 9 F.3d 576, 582 (7th Cir.1993), cert. denied, 513 U.S. 844, 115 S.Ct. 135, 130 L.Ed.2d 77 (1994). The Delapena Grand Jury testimony does not meet this test. Stretching materiality to its limits, one could argue that on some theory Delapena's absence of knowledge of an