Mental disorder defence
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In the criminal laws of Australia and Canada, the defence of mental disorder (sometimes called the defence of mental illness) is a legal defence by excuse, by which a defendant may argue they should not be held criminally liable for breaking the law because they were mentally ill at the time of the alleged criminal actions.
A person is mentally incompetent to commit an offence if, at the time of the conduct alleged to give rise to the offence, the person is suffering from a mental impairment and, in consequence of the mental impairment—
- (a) does not know the nature and quality of the conduct; or
- (b) does not know that the conduct is wrong; or
- (c) is unable to control the conduct.
269H—Mental unfitness to stand trial
A person is mentally unfit to stand trial on a charge of an offence if the person's mental processes are so disordered or impaired that the person is—
- (a) unable to understand, or to respond rationally to, the charge or the allegations on which the charge is based; or
- (b) unable to exercise (or to give rational instructions about the exercise of) procedural rights (such as, for example, the right to challenge jurors); or
- (c) unable to understand the nature of the proceedings, or to follow the evidence or the course of the proceedings.
In Victoria the current defence of mental impairment was introduced in the Crimes (Mental Impairment and Unfitness to be Tried) Act 1997 which replaced the common law defence of insanity and indefinite detention at the governor's pleasure with the following:
- the accused was suffering from a mental impairment; and
- the mental impairment affected the accused so he or she either did not understand the nature and quality of the conduct, or did not know that it was wrong.
These requirements are almost identical to the M'Naghten Rules, substituting "mental impairment" for "disease of the mind".
Subsequent Australian cases have qualified the M'Naghten Rules. The High Court in R v Porter stated that the condition of the accused’s mind is relevant only at the time of the actus reu. In Woodbridge v The Queen the court stated that a symptom indicating a disease of the mind must be prone to recur and be the result of an underlying pathological infirmity. A ‘defect of reason’ is the inability to think rationally and pertains to incapacity to reason, rather than having unsound ideas or difficulty with such a task. See also. 
The defence of mental disorder is codified in section 16 of the Criminal Code of Canada which states, in part:
- 16. (1) No person is criminally responsible for an act committed or an omission made while suffering from a mental disorder that rendered the person incapable of appreciating the nature and quality of the act or omission or of knowing that it was wrong. 
To establish a claim of mental disorder the party raising the issue must show on a balance of probabilities first that the person who committed the act was suffering from a "disease of the mind", and second, that at the time of the offence they were either 1) unable to appreciate the "nature and quality" of the act, or 2) did not know it was "wrong".
The current legislative scheme was created by the Parliament of Canada after the previous scheme was found unconstitutional by the Supreme Court of Canada in R. v. Swain. The new provisions also replaced the old insanity defence with the current mental disorder defence. 
Once a person is found not criminally responsible ("NCR"), he or she will have a hearing by a Review Board within 45 days (90 days if the court extends the delay). A Review Board is established under Part XX.1 of the Criminal Code of Canada and is composed of at least three members, a person who is a judge or eligible to be a judge, a psychiatrist and another expert in a relevant field, such as social work, criminology or psychology. Parties at a Review Board hearing are usually the accused, the Crown and the hospital responsible for the supervision or assessment of the accused. A Review Board is responsible for both accused persons found NCR or accused persons found unfit to stand trial on account of mental disorder. A Review Board dealing with an NCR offender must consider two questions: whether the accused is a "significant threat to the safety of the public" and, if so, what the "least onerous and least restrictive" restrictions on the liberty of the accused should be in order to mitigate such a threat. Proceedings before a Review Board are inquisitorial rather than adversarial. Often the Review Board will be active in conducting an inquiry. Where the Review Board is unable to conclude that the accused is a significant threat to the safety of the public, the review board must grant the accused an absolute discharge, an order essentially terminating the jurisdiction of the criminal law over the accused. Otherwise the Review Board must order that the accused be either discharged subject to conditions or detained in a hospital, both subject to conditions. The conditions imposed must be the least onerous and least restrictive necessary to mitigate any danger the accused may pose to others.
Since the Review Board is empowered under criminal law powers under s. 91(27) of the Constitution Act, 1867 the sole justification for its jurisdiction is public safety. Therefore the nature of the inquiry is the danger the accused may pose to the public safety rather than whether the accused is "cured." For instance, many "sick" accused persons are discharged absolutely on the basis that they are not a danger to the public while many "sane" accused are detained on the basis that they are dangerous. Moreover the notion of "significant threat to the safety of the public" is a "criminal threat." This means that the Review Board must find that the threat posed by the accused is of a criminal nature.
While proceedings before a Review Board are less formal than in court, there are many procedural safe-guards available to the accused given the potential indefinite nature of Part XX.1. Any party may appeal against the decision of a Review Board.
In 1992 when the new mental disorder provisions were enacted, Parliament included "capping" provisions which were to be enacted at a later date. These capping provisions limited the jurisdiction of a Review Board over an accused based on the maximum potential sentence had the accused been convicted (e.g. there would be a cap of 5 years if the maximum penalty for the index offence is 5 years). However, these provisions were never proclaimed into force and were subsequently repealed.
A Review Board must hold a hearing every 12 months (unless extended to 24 months) until the accused is discharged absolutely.
An accused who is found to be unfit to stand trial is subject to the jurisdiction a Review Board. While the considerations are essentially the same, there are a few provisions which apply only to unfit accused. A Review Board must determine whether the accused is fit to stand trial. Regardless of the determination, the Review Board must then determine what conditions should be imposed on the accused, considering both the protection of the public and the maintenance of the fitness of the accused (or conditions which would render the accused fit). Previously an absolute discharge was unavailable to an unfit accused. However, in R. v. Demers, the Supreme Court of Canada struck down the provision restricting the availability of an absolute discharge to an accused person who is deemed both "permanently unfit" and not a significant threat to the safety of the public. Presently a Review Board may recommend a judicial stay of proceedings in the event that it finds the accused both "permanently unfit" and non-dangerous. The decision is left to the court having jurisdiction over the accused.
An additional requirement for an unfit accused is the holding of a "prima facie case" hearing every two years. The Crown must demonstrate to the court having jurisdiction over the accused that it still has sufficient evidence to try the accused. If the Crown fails to meet this burden then the accused is discharged and proceedings are terminated. The nature of the hearing is virtually identical to that of a preliminary hearing.
- Settled insanity
- NCR: Not Criminally Responsible, a Canadian documentary film about the mental disorder defence
- R v Porter  HCA 1 Austlii
- Woodbridge v The Queen (2010) 208 A Crim R 503, 531 (Davies J)
- R v Porter  HCA 1 Austlii
- R v Cheatham  NSWCCA 282 Austlii
- "16. Defence of mental disorder".
- Pilon, Marilyn (2002), Mental Disorder and Canadian Criminal Law, Government of Canada, Law and Government Division, retrieved 10 September 2011