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Mental Impairment (Vic)

The defence of mental impairment is contained in the Crimes (Mental Impairment and Unfitness To Be Tried) Act 1997. Mental impairment is not defined by the Act but courts have often considered it to mean a severe mental illness or disorder. The Act recognises that if a person is mentally impaired, they will not have the capacity to be criminally responsible for their actions. This approach places the focus on rehabilitation rather than punishment. The mental impairment defence does not include impairment caused by drug or alcohol use.


Section 20 states the defence is established if the person’s mental impairment had the effect that they:

  • did not know the nature and quality of the conduct; or
  • did not know the conduct was wrong – that they “could not reason with a moderate degree of sense and composure about whether the conduct, as perceived by reasonable people, was wrong”.

The onus is on the accused person to prove they were suffering the impairment because the presumption is that they were not. The question of mental impairment can be raised at any time during a trial by the defence, or with the leave (permission) of the trial judge, by the prosecution.

Judge-only hearing

If the defence and prosecution agree the accused person was suffering from a mental impairment when they committed the offence, the matter will be heard by a judge without a jury. At the end of what is called a Consent Mental Impairment Hearing, after considering expert medical evidence, the judge can find the person not guilty due to their mental impairment, or order the person be tried in the usual way for a criminal matter because the judge is not satisfied the person has a mental impairment.

If a person is found not guilty due to mental impairment, the court must either declare the person is liable to a supervision order, or release them unconditionally. Unconditional release happens only in exceptional circumstances, when the court, after considering specialist medical advice, rules the person who committed the crime is not a danger to themselves or other people.

Trial before a jury

If the defence and prosecution do not agree the accused person was suffering from a mental impairment when they committed the crime, the matter will go to a trial before a jury.

If there is evidence that raises the question of mental impairment, a judge must direct the jury to consider the question, and explain the findings which can be made and the consequences of them. The jury will decide the person is guilty, not guilty, or not guilty because of mental impairment.

If the person is found not guilty, they are released from custody or discharged from bail. If the person is found guilty, they will be sentenced in the usual way. If the person is found not guilty due to their mental impairment, the judge will usually make a supervision order or release them unconditionally.

Pending the making of a supervision order, the court can order the person be released on bail, remanded in custody, or that they undergo a mental health assessment to be used by the court.

Supervision orders

A supervision order enables a person to be placed in appropriate care or receive treatment. A custodial supervision order means the person is held at a secure hospital to receive compulsory treatment. A non-custodial supervision order means the person is deemed a low risk to themselves or the community and receives treatment in the community, while subject to conditions.  Conditions can include that the person must:

  • attend regular appointments for medical treatment and testing;
  • not leave Victoria;
  • live at a specified address.

The Act allows for the emergency apprehension of a person subject to a non-custodial order by an approved person, such as a police or ambulance officer. An apprehension can be carried out if the approved person reasonably believes the supervised person has failed to comply with their supervision order or that the safety of the supervised person or the public is at risk if the supervised person is not apprehended.


A person has a right to appeal a finding of mental impairment made against them. An appeal must be lodged within 28 days of the verdict unless a time extension is granted. The appeal must be granted if the court is satisfied:

  • the verdict is unreasonable or not supported by evidence; or
  • there has been a substantial miscarriage of justice as the result or an error or irregularity in the trial, or for any other reason.

The court of appeal can substitute a guilty verdict and make an order; enter a judgment and verdict of acquittal; or order a new trial.

The Director of Public Prosecutions can appeal against an order for the unconditional release of a person found guilty due to mental impairment, if the director considers the order should not have been made and an appeal should be made in the public interest. The court can either confirm the order or set it aside and declare the person is liable to a supervision order. It can make a supervision order itself or remit the matter to the original court for this.

For advice or representation, please contact Armstrong Legal.

Sally Crosswell

This article was written by Sally Crosswell

Sally Crosswell has a Bachelor of Laws (Hons), a Bachelor of Communication and a Master of International and Community Development. She also completed a Graduate Diploma of Legal Practice at the College of Law. A former journalist, Sally has a keen interest in human rights law.

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