What is the test for a conviction for aiding and abetting a criminal offence?

A conviction for aiding and abetting requires proof that the accused had the intent required for the underlying substantive offense. United States v. Litteral, 910 F.2d 547, 550 (9th Cir.1990). The substantive offense of mail fraud requires knowledge of the fraudulent purpose. See United States v. Price, 623 F.2d 587, 591 (9th Cir.), cert. denied, 449 U.S. 1016, 101 S.Ct. 577, 66 L.Ed.2d 475 (1980), overruled on other grounds, United States v. De Bright, 730 F.2d 1255, 1259 (9th Cir.1984) (en banc).