US Criminal Law/Defenses/Insanity defense

The insanity defense is a rarely used legal argument. It is based upon the claim the defendant is suffering from a mental illness or mental incapacity. Under one of the rules for determining insanity, the M'Naghten rule, the defendant is considered not guilty if at the time of the crime the person did not know what he was doing or did not know what he was doing was wrong. While there are several other rules for determining insanity all of them focus upon the person not being fully aware of what they were doing or that the action was wrong because of a mental illness. If the person is found not guilty by reason of insanity the judge may order the person to be committed for psychiatric treatment until they are cured.