The Defence of Mental impairment
The defence of mental impairment is a complete defence to any criminal offence in Victoria. The defence of mental impairment arises when an accused person has a mental illness which can include, senility, intellectual disability, brain damage or severe personality disorder, and as a result of that mental illness, the accused person does not know what they are doing, or if they know what they are doing, they do not understand that it is wrong.
In Victoria the defence of mental impairment is governed by the Crimes (Mental Impairment and Unfitness to the Tried) Act 1997 (CMIA). The current defence was created by s 20 of the act and applies to all criminal offences alleged to have been committed on or after 18 April 1998. Previously the defence was called the ‘insanity defence’ governed by the common law ( now repealed by s 25 of the act).
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. The defence of mental impairment exists so that individuals are not held criminally responsible for offending that occurs because of an impairment that has seriously affected their mental capacity. These principles of fairness have existed in the common law for centuries, giving rise to the defence of mental impairment.
What is mental impairment?
The term ‘mental impairment’ is not defined by legislation however the common law has held the term to have the same meaning as “disease of the mind” which formed the basis of the common law insanity defence (R v Sebalj  VSC 181, DPP V Taleski  VSC 183, R v Martin  VSC 518.
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. In Falconer  and R v Radford (1985) a “disease” of the mind was determined as connoting an unhealthy or “inform” mind, as opposed to a healthy mind affected by a transient, non- recurrent mental malfunction caused by external forces.
The cases of R v Hughes (1989), R v Falconer (1990), and Nolan v R (1997) held that a disease of the mind could include the following:
- Brain injuries
- Episodes of dissociation
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 .
What is a mental impairment defence?
The defence of mental impairment can be raised at any time during the trial either by the defence or the prosecution – s 22(1), Hassan  VSC 85). The accused person bears the burden of proof of and must provide evidence that supports the defence of mental impairment. The evidence provided to the court is usually medical reports prepared by experts who may also be required to give evidence on the issue of mental impairment.
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 —
- he or she did not know the nature and quality of the conduct; or
- he or she did not know that the conduct was wrong (that is, he or she could not reason with a moderate degree of sense and composure about whether the conduct, as perceived by reasonable people was wrong).
If the defence of mental impairment is established, the person must be found not guilty because of mental impairment – see s 20(2) of the Crimes Mental Impairment and Unfitness to be Tried) Act 1997.
The standard of proof is on the balance of probabilities which means that it is more probable than not that an accused person was suffering from a mental impairment at the time of the offending see R v Whelan . The balance of probabilities is a lower standard than beyond a reasonable doubt which is the threshold that needs to be established by Prosecution for most criminal offences.
Nature and quality of the conduct regarding mental impairment
The ‘nature and quality of the conduct’ 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).
While 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).
In contrast to the defence of mental impairment, which is relevant to a person’s conduct at the time of the offence, sometimes an investigation is required to determine if an accused person is mentally fit to stand trial ( see s 11) In some cases there may be an investigation into both issues.
What is the court process for mental impairment matters?
If prosecution and defence agree that the accused was suffering from a mental impairment at the time they committed a crime the matter will be heard by a judge without a jury. This is called a consent mental impairment hearing. This usually occurs when both defence and prosecution agree on the findings of specialist medical evidence that has been provided to the court.
Following a consent mental impairment hearing a judge can make the following orders:
- Find the person not guilty because of their mental impairment
- Direct that the accused person be tried in the usual way if they are not satisfied that the accused person has a mental impairment
If prosecution and defence do not agree that the accused was suffering from a mental impairment there will be a trial before a jury where expert evidence is called.
The jury will need to determine the following:
- Whether the accused is guilty or not guilty of the crime
- Whether the accused person committed the crime but is not guilty because of their mental impairment
If an accused person is found not guilty, they will be acquitted of the offence. If the accused person is found guilty, they will be sentenced by a judge in the ordinary way like any other criminal matter. If the accused person is found to have committed the crime but is not guilty because of their mental impairment, usually the judge will place the person on a supervision order. A supervision order enables a person to be held in appropriate care or in the community to receive treatment. The length of a supervision order can carry the same maximum duration as the maximum term of imprisonment of the offending.
The court also has the power to unconditionally release the offender however this is rare and would only occur if the offender is not a danger to him or herself or the community.
In the Magistrates’ Court the process is different. If a magistrate finds a person not guilty because of mental impairment the court must discharge the person which means no penalty is imposed.
The defence of mental impairment 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.