As Americans speculate about why a young man in Colorado allegedly engaged in a nightmarish shooting rampage in a movie theater, lawyers for a convicted killer in Idaho are asking the Supreme Court to rule that states must allow defendants to plead not guilty by reason of insanity. The court should do so.
James Holmes, the 24-year-old former graduate student accused of killing 12 people and injuring 58 during a midnight showing of "The Dark Knight Rises," could face the death penalty if convicted. But, like defendants in 46 states, Holmes will be able to plead insanity. In Colorado, a defendant is legally insane if he is "so diseased or defective in mind at the time of the commission of the act as to be incapable of distinguishing right from wrong."
An insanity defense is rarely asserted, and the definition of legal insanity varies from state to state. Half the states, including California, employ a variation of the M'Naghten Rule adopted by the British House of Lords in an 1843 murder case: A defendant is insane if at the time of the crime he either didn't know that what he was doing was wrong or was unable to understand the nature and quality of his act. Other states use a broader definition that defines insanity as the inability of a defendant, because of mental illness, "to conform his conduct to the requirements of the law."