Staggs was wanted for desertion from the U.S. Marine Corps. Two F.B.I. agents came to arrest Staggs in Illinois. They were permitted entry to his apartment by his wife. The agents called out to Staggs, and when one of them peaked into the bedroom where he was located, he observed Staggs standing in the corner holding a gun with both hands which he pointed at the agent. Staggs made statements about not going back and that if anyone came into the bedroom, he would shoot them. Staggs (D) was charged with violation of 18 U.S.C. Section 111. At trial, he testified that he had not intended to hurt any of the agents and intended to use the gun on himself. The Court excluded testimony from a Dr. William Sloan, a psychologist, who had examined D. The Dr. offered to testify that D was more likely to hurt himself than others. D was convicted and appealed.