Definition - What does Criminal Insanity mean?
Criminal insanity is when a person is of such a profound state of mental incompetence that they cannot be held accountable for a crime. Insanity is a form of mental illness in which the afflicted person does not have a sufficient enough grasp of reality to be considered rational. Because conscious knowledge of one's actions is required to be held accountable for a crime, the criminally insane cannot be found guilty
Justipedia explains Criminal Insanity
If a person is considered criminally insane, it means that even if they committed a crime, then they cannot be held accountable. This can lead to an insanity defense in a criminal trial. For example, if an insane person assaulted another person, their lawyer may choose to try to plead insanity in order to prevent the defendant from being held accountable. If the defendant is found not guilty by reason of insanity, then they won't go to prison. However, they could still be forced to go to a psychiatric hospital until they are deemed no longer a threat to society.