Defence of Mental Impairment

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Gabrielle RedmondThe article Defence of Mental Impairment is written by Gabrielle Redmond, Lawyer, Doogue + George Defence Lawyers.

Gabrielle Redmond was admitted to Australian legal practice in 2019 and passed the New York bar exam in February 2020. She graduated with a Bachelor of Laws with Honours and Bachelor of Creative Industries majoring in Music from the Queensland University of Technology.

Prior to joining Doogue + George, Gabrielle worked as a legal assistant and, subsequently, a lawyer at Furstenberg Law where she assisted with criminal and confiscation matters. She also started her Master of Laws at the University of Melbourne in 2021.


CT Scan of Someone With Mental ImpairmentIn Victorian criminal law, there is a defence of mental impairment. This defence can be raised by people who have been charged with criminal wrongdoing. If it is found that an accused person was mentally impaired at the time of committing an offence, then the accused may be found not guilty by reason of mental impairment.

The legislation that gives rise to this defence is the Crimes (Mental Impairment and Unfitness to be Tried) Act 1997 (VIC). The purpose of this legislation is to deal with cases that involve people who are so significantly affected by their mental condition that they require a specialised response from the law. In this article, we take a brief look at the power of this legislation with a specific focus on the defence of mental impairment.

Old English Roots

While the defence of mental impairment is contained in the Act, this defence has English roots.

In 1943, Daniel M’Naghten was accused of murdering the Secretary to the English Prime Minister after shooting him in the street. M’Naghten was a political activist who was said to have paranoid delusions about the Tory Party. At trial, both the prosecution and defence agreed that M’Naghten suffered from delusions of persecution. M’Naghten was ultimately acquitted on the grounds of ‘criminal insanity’. His case informed the defence of mental impairment and the common law presumption of sanity – that is, everyone is presumed to be sane unless proven otherwise on the balance of probabilities.

Establishment of the Act

Prior to the introduction of the Act in Victoria, a person found not guilty or unfit to plead guilty on the ground of insanity could be detained under indefinite orders under the Governor’s pleasure regime. Under this system, people were frequently left in custody until the Attorney-General reviewed their matter and decided they were fit for release. There was no transparency in this archaic process, and it left vulnerable people languishing in custody indefinitely. The regime was abandoned in 1997 with the introduction of the Act in Victoria. The goal of the act was to balance the rights of people whose disabilities meant they lacked usual legal culpability or capacity with the expectations of the community’s expectation of security and safety.

Mental impairment is not actually defined in the Act. However, it’s defined in case law as a ‘disease of the mind’. The Commonwealth Criminal Code 1995 notes that mental impairment includes senility, intellectual disability, mental illness, brain damage and severe personality disorder. A mental impairment may be permanent or temporary, curable or incurable.

Supervision Orders

While the Governor’s pleasure regime has been abandoned, under the Act, the court can impose a supervision order on a person with a mental impairment for an indefinite term. A supervision order may:

  1. commit the person to custody
  2. commit the person to an ‘appropriate place’
  3. commit the person to prison if there are no practicable alternatives

When making a supervision order, the court may direct that the matter be brought back to the court for review at the end of the period specified by the court. The Act lists matters that must be considered when sentencing a person with a mental impairment to a supervision order:

  1. The nature of the person’s mental impairment or other condition or disability;
  2. The relationship between the impairment, condition or disability and the offending conduct; and
  3. Whether the person is likely to endanger themselves or another person or persons because of his mental impairment;
  4. The need to protect people from such danger;
  5. Whether there are adequate resources available for the treatment and support of the person in the community; and
  6. Any other matters the court thinks relevant.

Case Examples

DPP v Ali:

In response to a matter where an accused man was charged with consistently assaulting sex workers, the judge was tasked with ordering an appropriate sentence. The judge considered the likelihood of the accused of posing a risk of endangering himself or others because of his mental impairment. This was with reference to the nature and repetition of the offending, the accused’s ongoing denial and lack of insight into the offending and the broader context of his cognitive deficits and history of drug and alcohol abuse. The accused man had no prior convictions, no family and few support opportunities in the Australian community. The accused wasn’t eligible to receive support under Forensicare, DHHS and NDIS as he was an unlawful non-citizen. The judge balanced the need to protect the community from sexual offending and noted the seriousness of the significance of the consequences for the victims.

The judge referred to section 26(4) of the Act, which dictates that the accused must not be committed to custody in a prison unless satisfied that no practicable alternative exists.

Given the lack of supports available to the accused, the only alternative was for the accused to be sent to immigration detention. The judge considered this to be a restrictive but secure environment for the accused which would limit his freedom while also addressing the issues of risk of endangerment and community protection. The accused was released on a non-custodial supervision order. He was required to immediately surrender himself to immigration detention.

DPP v Pidgeon:

In the matter of DPP v Pidgeon, the accused was charged with arson. The defence and prosecution agreed that the defence of mental impairment was available as the accused suffered from schizophrenia at the time of the offence. A mental impairment hearing was held, and the defence provided evidence to show that the accused was not guilty on the basis of the mental impairment defence. The judge was of the view that the accused was receiving adequate support in the community and ordered he be unconditionally released.

R v Munze:

In the case of R v Munze, the accused was charged with murdering his wife. The accused, who was 83 years old, was found lying next to his wife in a confused and dehydrated state nearly a week after allegedly killing her. Importantly, days before the alleged murder, the accused had done a brain scan which showed normal results. After the accused was arrested, a new brain scan showed bleeding on the brain. His lawyers explained the possibility that the accused was mentally impaired at the time of the alleged killing because of this bleed. By raising the defence of impairment, the defence had a duty to convince the trial judge that it was more probable that the accused had a brain injury – a mental impairment – at the time of the offending. The judge was not satisfied that it was more probable that the accused was mentally impaired at the time of killing his wife. The defence of mental impairment wasn’t available to the accused, and he was found to be unfit to stand trial due to his brain injury.

It’s important to consider the safety and protection of people directly impacted by or suffering from mental impairment as well as protection of the wider community. In our role as criminal defence lawyers, we take a strong interest in our client’s mental wellbeing and medical history. The Act attempts to balance the right of vulnerable of people in our criminal justice system. It is disheartening that there is still no guaranteed limit on the period of detention or supervision for a person with mental impairment. However, we hope that Victorian legislation continues to evolve to improve this important balance and increase transparency in the process.

Get in touch with Doogue + George lawyers on (03) 9670 5111 if you are unsure as to whether this defence is available in your case.

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