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The Defence Of Insanity (WA)


A person cannot be found guilty of a criminal offence if at the time, they were so mentally unwell that they did not understand what they were doing or could not control what they were doing. The defence of insanity is designed to balance the need to hold citizens accountable for their actions with a recognition that a person cannot be blamed for actions done when they were not in control of themselves. This article outlines the defence of insanity as it applies in Western Australia, as well as the process of establishing an accused person’s fitness for trial.

Defence of insanity vs unfitness for trial

The issue of whether an accused person has a defence of insanity available to them is separate to the issue of whether or not they are fit for trial. However, in some cases where unsoundness of mind is an issue, both of these questions may need to be determined.

The defence of insanity concerns the mental state of the accused at the time of the alleged offence; in contrast, the issue of fitness for trial concerns the mental state of the accused at the time of the court proceedings.

A person may have a defence of insanity available to them but be fit for trial by the time the matter has come to court. Similarly, a person may not have a defence of insanity available to them, but nonetheless be unfit for trial at the time the matter is being dealt with by a court.

Fitness for trial

Under section 9 of the Criminal Law (Mentally Impaired Accused) Act 1996, an accused person may be found not to be mentally fit to stand trial if:

  1. they do not understand the nature of the charge;
  2. they do not understand the requirement to enter a plea;
  3. they do not understand the purpose of a trial;
  4. they do not understand there right to challenge jurors;
  5. they are unable to follow the course of a trial;
  6. the are unable to understand the substantial effect of the evidence presented by the prosecution; or
  7. they are unable to properly defend the charge.

An accused person is presumed to be mentally fit to stand trial until the contrary is found.

The court will generally request that a fitness to plead report be prepared prior to considering whether an accused is fit to stand trial. This is a report prepared by a psychiatrist or other appropriately qualified professional after examining the accused person.

If an accused person is found to be fit for trial, the matter can proceed to be determined by a jury. If an accused is unfit for trial, they cannot be found guilty of an offence and must be dealt with outside of the criminal justice system. This may include being detained under the Criminal Law (Mentally Impaired Accused) Act 1996.

What is the defence of insanity?

If the accused is fit for trial and the defence believes that they were not of sound mind at the time the offence is alleged to have occurred, the defence of insanity will need to be explored. Under section 27(1) of the Act, a person is not criminally responsible for an act or omission on if at the time of doing the act or making the omission they were in such state of mental impairment as to deprive them of the capacity to understand what they were doing, of capacity to control their actions, or of capacity to know that they ought not to do the act or make the omission.

The Act also provides a defence if the accused is suffering from delusions. It states that a person whose mind, at the time of doing or omitting to do an act, is affected by delusions on some specific matter or matters, but who is not otherwise entitled to the benefit of unsoundness of mind, is criminally responsible for the act or omission to the same extent as if the real state of things had been such as they were induced by the delusions to believe to exist.

Raising the defence of insanity

Every accused person is presumed to be of sound mind. In Western Australia, this presumption is found in section 26 of the Criminal Code.

If an accused person wishes to rely on the defence of insanity, the defence has the burden of proving that the accused was not of sound mind at the time of alleged offence. This must be established on the balance of probabilities.

Whether or not an accused person is afforded a defence under section 27 of the Act is a question of fact. A question of fact can only be determined after a hearing of all the evidence.

Expert evidence

In order to find a person not guilty on the basis of the defence of insanity, the court must be satisfied that they were of unsound mind at the time of the alleged offending. This will generally be determined with reference to expert evidence.

The effect of the defence of insanity

If the defence of insanity is established, the accused will be acquitted of the offence. However, this does not mean that they will be free to go. If a person is found to be of unsound mind, but the objective elements of the offence are established, the person may be made subject to orders under the Criminal Law (Mentally Impaired Accused) Act 1996. This may include a lengthy or indefinite period of detention.

If you require legal advice or representation in any legal matter, please contact Armstrong Legal. 

This article was written by Courtney Ashton - Associate - Perth

Courtney holds a Bachelor of Laws and a Bachelor of Criminology and Justice from Edith Cowan University and a Graduate Diploma of Legal Practice from the College of Law. Courtney is a dedicated practitioner who enjoys a challenge and has competently completed many traffic and summary jurisdiction matters. Courtney enjoys advocacy and has appeared in a number of drink driving,...

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