The Durham rule states that an accused is not criminally responsible if his unlawful act was the product of mental disease or mental defect. The Durham rule was eventually rejected by the federal courts, because it cast too broad a net. Alcoholics, compulsive gamblers, and drug addicts had successfully used the defense to defeat a wide variety of crimes.
The federal insanity defense, established by the Comprehensive Crime Control Act, now requires the defendant to prove, by "clear and convincing evidence," that "at the time of the commission of the acts constituting the offense, the defendant, as a result of a severe mental disease or defect, was unable to appreciate the nature and quality or the wrongfulness of his acts".
