Mental Illness


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In cases where you were suffering from a mental impairment at the time of the offence, you may be able to raise the defence of mental illness.

The defence of mental illness is able to be raised for serious crimes such as murder, and, if raised successfully, will result in you being found ‘not guilty by reason of mental illness.’

If you wish to raise this defence, you will need to show evidence to prove on the balance of probabilities (that is, more than 50%) that:

1. You acted under a ‘defect of reason’ due to a ‘disease of the mind’

A ‘disease of the mind’ refers to a mental illness that results in violence and is likely to recur. You will have to prove that you suffered from the mental illness at the time of the offence, and, because of the mental illness, you did not understand that what you were doing was wrong according to the standards of a reasonable person.

The law recognises a wide range of ‘mental illnesses’ – they can be temporary or ongoing, curable or incurable.

However, you won’t be able to raise the defence of mental illness where there was some other external factor or influence on your mind – for example, where you were acting under the influence of drugs or alcohol.

The defence of mental illness is not one to be raised lightly. If you are successful in raising the defence, you will be found ‘not guilty by reason of mental illness,’ however, to protect the community the court may order that you be detained in a mental institution until you are fit to be released. Where it is shown that your mental illness is incurable, you may be detained in such an institution indefinitely.