Rider (D) went to kill Tallent for having committed adultery with D's wife. D armed himself with a gun and found Tallent. When Tallent attempted to strike him with an ax, D shot and killed him. At trial, D claimed that he shot in self-defense. The physical evidence supported D's version of the incident. The trial judge instructed the jury that D should be found guilty by the mere existence of prior intent and the later act of killing. D was convicted and appealed.