<P> Exemption from full criminal punishment on such grounds dates back to at least the Code of Hammurabi . Legal definitions of insanity or mental disorder are varied, and include the M'Naghten Rule, the Durham rule, the 1953 British Royal Commission on Capital Punishment report, the ALI rule (American Legal Institute Model Penal Code rule), and other provisions, often relating to a lack of mens rea ("guilty mind"). In the criminal laws of Australia and Canada, statutory legislation enshrines the M'Naghten Rules, with the terms defense of mental disorder, defense of mental illness or not criminally responsible by reason of mental disorder employed . Being incapable of distinguishing right from wrong is one basis for being found to be legally insane as a criminal defense . It originated in the M'Naghten Rule, and has been reinterpreted and modernized through more recent cases, such as People v. Serravo . </P> <P> In the United Kingdom, Ireland, and the United States, use of the defense is rare; however, since the Criminal Procedure (Insanity and Unfitness to Plead) Act 1991, insanity pleas have steadily increased in the UK . Mitigating factors, including things not eligible for the insanity defense such as intoxication (or, more frequently, diminished capacity), may lead to reduced charges or reduced sentences . </P> <P> The defense is based on evaluations by forensic mental health professionals with the appropriate test according to the jurisdiction . Their testimony guides the jury, but they are not allowed to testify to the accused's criminal responsibility, as this is a matter for the jury to decide . Similarly, mental health practitioners are restrained from making a judgment on the issue of whether the defendant is or is not insane or what is known as the "ultimate issue". </P> <P> Some jurisdictions require the evaluation to address the defendant's ability to control their behavior at the time of the offense (the volitional limb). A defendant claiming the defense is pleading "not guilty by reason of insanity" (NGRI) or "guilty but insane or mentally ill" in some jurisdictions which, if successful, may result in the defendant being committed to a psychiatric facility for an indeterminate period . </P>

Who must determine whether a defendant was insane at the time of a crime