What is the test for determining whether an assault on a federal officer is a criminal act if the assailant had no knowledge of the officer's duty status?

The assailant need intend only to assault one who later proves to be a federal officer. United States v. Freie, 545 F.2d 1217, 1222 (9th Cir.), cert. denied, 430 U.S. 966, 97 S.Ct. 1645, 52 L.Ed.2d 356 (1977). The assailant's knowledge of the officer's duty status is irrelevant. Cf. United States v. Yermian, 468 U.S. 63, 68-69, 104 S.Ct. 2936, 2939, 82 L.Ed.2d 53 (1984) (quoting Feola as holding: " 'existence of fact that confers federal jurisdiction need not be one in the mind of the actor at the time he perpetrates the act made criminal by the federal statute.' ").