Not guilty by reason of insanity
The M’Naghten defense was the first case to judicially determine whether a defendant at the time of the crime was legally insane.
Under M’Naghten, a defendant is considered legally insane if the accused was mentally or emotionally incapable of differentiating between right and wrong when the crime was committed.
The irony behind the M’Naghten test is that the court had first to make a finding that the defendant, despite his insanity defense, was, in fact, mentally competent to stand trial. To add clarity and uniformity to the insanity test, a new rule was developed to determine insanity and was made part of the Modern Penal Code.
MPC Section 401 essentially states:
A defendant is not legally responsible for their criminal conduct where, because of a “mental disease or defect,” the defendant neither possessed nor had a substantial mental capacity to appreciate the criminality of their conduct nor was able to conform his conduct to the law.
