Section 269C of the Criminal Law Consolidation Act 1935 (SA) outlines a general defence of Mental Impairment, where because of a mental illness, intellectual disability or a disability or impairment of the mind resulting from senility, the defendant did not know the nature and quality of their conduct or could not reason that what they did was wrong or were totally unable to control their conduct.

The law recognises that such persons do not have the mental element of a guilty mind that is required to be found guilty of a criminal offence.

Parties must inform the relevant court as soon as practicable however if questions arise about the mental competence of a defendant to commit the offence charged [Joint Criminal Rules 2022 (SA) r 67.2]. If a lawyer has reason to believe that their client may have been mentally incompetent to commit the offence charged, the lawyer must expeditiously inquire into these matters.

Sub-section 269C(2) sets out that where a person is found to be mentally incompetent to have committed the offence, but the trial judge is satisfied, on the balance of probabilities, that the mental impairment was substantially caused by self-induced intoxication, the person may be dealt with instead under Part 8, see Intoxication. Sub-sections 269A(2a) and (2b) states that intoxication resulting from recreational use of drugs or the combined effect of therapeutic and recreational use is to be regarded as self-induced. Sub-section 269C(3), however, does allow for the court to make an order that a person whose mental impairment was substantially caused by self-induced intoxication still be dealt with under the mental impairment provisions of Part 8A of the Act [see s 269C(3)]. The court can make such an order where it is in the interests of justice to do so, and taking into account whether the making of such an order would affect public confidence in the administration of justice [s 269C(3)].

There is a presumption of mental competence [s 269D] and to make use of the mental impairment defence, mental incompetence must be shown on the balance of probabilities. The possible consequences of a finding of mental impairment are unconditional release or release on strict conditions of supervised licence or detention in secure psychiatric care [ss 269NB and 269O]. It is a condition of every licence for release that the defendant be prohibited from possessing firearms and ammunition. The Court may also direct a defendant to surrender a firearm [ss 269NC and 269OA]. When determining whether to release a defendant, either unconditionally or on a licence, the paramount consideration must be the safety of the community [ss 269NA and 269NI].

Supervision orders are governed by Chapter 2 Part 2 of the Uniform Special Statutory Rules 2022 (SA).