D and his confederates arranged for a sale of heroin to buyers who turned out to be federal undercover agents. D planned to palm off on the purchasers, for a substantial sum, a form of sugar in place of heroin and, should that ruse fail, simply to surprise their unwitting buyers and relieve them of the cash they had brought along for payment. The plan failed when one agent, his suspicions being aroused, drew his revolver in time to counter an assault upon another agent from the rear. D was charged with conspiring to assault and with assaulting federal agents. The trial court read instructions to the jury that there was no need to conclude that D even knew that the agents were federal agents to convict of a conspiracy to assault a federal officer. D was found guilty. The court of appeals reversed; knowledge of the victim's official identity must be proved in order to convict on such a conspiracy charge. The Appeals court relied on Judge Learned Hand's opinion in United States v. Crimmins, 123 F.2d 271 (CA2 1941), holding that scienter of a factual element that confers federal jurisdiction, while unnecessary for conviction of the substantive offense, is required in order to sustain a conviction for conspiracy to commit the substantive offense.