The Defence of Mental impairment
In Victoria, the defence of mental impairment is governed by the Crimes (Mental Impairment and Unfitness to the Tried) Act 1997 (CMIA).
The defence of mental impairment is used where a person charged with an offence, at the time of engaging in behaviour constituting the offence, was suffering from a mental impairment that had the effect that they either—
- did not understand the nature and quality of what they were doing; or
- did not know what they were doing was wrong.
Criminal responsibility relies on the assumption that all people have the cognitive capacity to make rational decisions and are aware of the consequences and significance of their actions. This notion is not valid in the context of mental impairment. In these circumstances, the criminal law does not hold these impaired people accountable for their actions. A person should not be punished for an offence if they are not criminally responsible for the conduct because of mental impairment, however, at the same time, the community must be protected from the risk posed by people because of their mental impairment. These principles have existed in the law for centuries. Giving rise to the defence of mental impairment.
Operational elements of mental impairment
The test for the defence of mental impairment has two operational elements or limbs (the M’Naghten Rule) that are included in section 20 of the CMIA. The test requires that at the time of offending one or both of the elements were present. The first of these limbs focuses on the nature and quality of the act; this may be the physical nature of the act or the consequences of the behaviour. Here the accused does not know the nature of their conduct; this is rare. The second relates to comprehending that the act is wrong. It looks at the capacity of the accused in processing knowledge about the nature and quality of their conduct in terms of it being unreasonable in the community.
Nature and Quality of the Act
Nature and quality of the act is the limb that focuses on the accused’s capacity to comprehend cause and effect and to understand the characteristics and significance of objects that surround them. The accused must also have been unable to appreciate the physical nature of what s/he was doing. This component is satisfied where the accused’s cognitive capabilities are so lacking that s/he cannot distinguish between animate and inanimate objects (as by treating a doll as a live child) or understand the possible outcome of his or her actions (as giving an intoxicating substance to an infant as a means of soothing it): see Porter v The Queen (1933).
The accused may know the nature and quality of her/his act, s/he still may not know that the act is wrong. The question is whether or not the accused appreciated at the time of committing the act, that the act was wrong regarding the standards of reasonable people: see Stapleton v The Queen (1952). The focus is on what is morally wrong, and the test is to ascertain whether the accused appreciated that their act was wrong according to the ordinary standards of reasonable people; not whether they were capable of understanding the action was illegal. It means ‘wrong’ in the normative rather than the legal sense. The issue is, was the accused capable of reasoning about right and wrong in the same way ‘ordinary reasonable people’ do as opposed to his/her individual beliefs: see R v Porter (1933).
What is Mental Impairment?
In Victoria, the term ‘mental impairment’ is held to have a similar connotation to ‘disease of the mind’ as in the defence of automatism. The term’ disease of the mind’ is quite broad. It is a legal rather than a medical term and consequently extends beyond medically recognised psychiatric conditions. There is debate about which conditions constitute a disease of the mind for the purposes of the mental impairment defence, and it has been argued that legal definitions of what constitutes a mental condition at law are generally unclear and variable. The cases of R v Hughes (1989), R v Falconer (1990), and Nolan v R (1997) provided that brain injuries, tumours, and episodes of dissociation and epilepsy are examples of diseases of the mind. Permanent, not transient infirmity; it must be an unhealthy mind, as opposed to a healthy mind affected by a temporary mental glitch caused by external forces: R v Falconer  and R v Sebalj .
A temporary state of intoxication does not constitute a ‘disease of the mind’. Even if the effects of intoxication were so strong that the accused did not know what they were doing or that it was wrong. Nor will it be a defence if the accused became intoxicated knowing it would trigger a disease of the mind. Though in limited circumstances the requirements of the defence may be met if the consumption of drugs or alcohol caused, triggered or exacerbated a condition which is considered to be a ‘disease of the mind’ (for example schizophrenia) in an unsuspected person: see R v Stones (1955); R v Shields ; R v Meddings .
Presumptions and Standard of Proof
Pursuant to section 21 of the CMIA, a person is presumed not to have been suffering from a mental impairment having the effect referred to in section 20(1) until the contrary is proved. The question whether a person was suffering from a mental impairment is a question of fact and is to be determined by the trier of fact on the balance of probabilities: see R v Whelan . It is a question that may be raised at any time during a trial by the defence or by the prosecution: see R v Hassan .
The onus of rebutting the presumption of soundness of mind rests on the party raising the question of mental impairment. In most instances it is the defence that raises the issue, and they will be required to prove that the accused was mentally impaired at the time of offending. However, the burden will rest on the prosecution if they raise the issue under section 22 of the CMIA. The trier of fact must also be satisfied that the accused did engage in the “conduct constituting the offence”. Section 3(1) of the CMIA states that “conduct includes doing an act and making an omission”. Thus, the prosecution must prove, beyond a reasonable doubt, that the accused committed the act or omission which constitutes the offence charged.
When a finding is made in relation to mental impairment;
The defence of mental impairment applies to summary offences and indictable offences heard and determined summarily. The defence can be raised in the Magistrates’ Court when considering the criminal responsibility of the accused for an offence. The CMIA states the following
- if a Magistrate finds a person not guilty because of mental impairment for a summary offence or an indictable offence triable summarily, the Court must discharge the person.
- An accused will not be discharged in a committal proceeding because the defence is raised.
- The Magistrates’ Court has no power to make orders in relation to people found not guilty because of mental impairment unlike the higher courts.
- In the higher courts successfully pleading the accused was suffering from mental impairment at the time of offending will result in the accused being found not guilty due to mental impairment and placed on a supervision order, the maximum duration of which is the maximum term of imprisonment for the offence with which the accused was charged: section 27 CMIA.
The current requirements to establish the defence of mental impairment under the CMIA are that at the time of the commission of the offending conduct, a person has a mental impairment, characterised as a ‘disease of the mind’. And that mental impairment had at least one of two effects on the accused, they did not know the nature and quality of their conduct, or they did not know that their conduct was wrong. The defence is complicated and despite the prevalence of mental illness and cognitive impairment in those charged with criminal offences it is rarely utilised as a full defence for a number of reasons. Please be aware that the above document is not legal advice. If you have been charged with criminal offending and feel that mental illness has played a role please make an appointment with one of our specialist criminal lawyers to discuss your case.