Crimes involving mental illness or impairment

From time to time, the courts have to consider whether the accused is capable of taking part in the legal process and / or can be held responsible for their actions.

This might be because of mental illness, an intellectual disability, dementia, or another mental impairment.

The courts deal with these matters differently to other criminal matters. There is also a different process when the crime is a serious (‘indictable’) offence to when it is a less serious (‘summary’) offence.

It can add to the stress victims and other witnesses are already experiencing when the accused isn’t dealt with in the ordinary way under criminal law. So you know what is ahead, we have described the different paths that matters involving mental illness or impairment can take. (This information is also available in a brochure.)


Why the courts treat these matters differently​Graphic of child's head inside man's


A person cannot be found guilty of a crime if they didn’t understand at the time that what they were doing was ‘wrong’ by normal community standards.

Also, to be put on trial, a person has to be capable of understanding the charges against them and of taking part in court proceedings – that is, they have to be ‘fit to be tried’. This is part of making sure that everyone who goes on trial gets a fair trial.

For these reasons, the courts take a different approach to criminal matters if there are questions about the accused’s mental health or capacity when the offence was committed, or when they are facing court. In NSW, the system set up by the Mental Health (Forensic Provisions) Act 1990 will usually apply.

How this affects you

It’s important for victims and witnesses to know that the legal steps, the verdict and the penalties can all be different in these matters than in other criminal matters.

The prosecution process can become very complex and take a long time, sometimes years, to finalise.

One of the differences that affects you directly is that you will not to be called to give evidence in a trial if the accused is not fit to be tried. However, if the offence is serious and the judge holds what is called a ‘special hearing’ you will give evidence.

Steps when mental illness or impairment questions raisedIf the judge holding the fitness inquiry finds the accused is fit to be tried, the matter will go back to where it was in the criminal justice system and continue like any other criminal matter. For example, if it was at the committal stage in the Local Court, it will return there. If the accused was on trial in the District or Supreme Courts, the trial process will continue.

A ‘fit to be tried’ finding does not mean the accused’s mental condition won’t be raised again. During a trial or a sentence hearing, or in a ‘special hearing’, the court may still hear evidence about the accused’s mental state at the time the offence occurred (see Mental illness / impairment as a defence below).

If the accused is found unfit to be tried, a panel of mental health experts called the Mental Health Review Tribunal (MHRT) will assess whether they are likely to become ‘fit’ within the next 12 months.

A person could become fit, for example, if they had stopped taking medication for a condition such as schizophrenia and begin taking it again.

If the MHRT finds it is likely the accused will become fit to be tried within 12 months, the court will either release them on bail for up to 12 months (on the condition they receive mental health treatment and support) or detain them for up to 12 months – in custody, a prison hospital or a mental health facility.

The MHRT will assess the accused regularly after the fitness inquiry and advise the court when they become fit to go on trial. The court will then hold another fitness inquiry. If the judge agrees with the MHRT that the accused has become ‘fit’, the matter will go back to the criminal justice system and continue like any other criminal matter.Accused is unfit but likely to become fit


Process when accused is unlikely to become fitIf the MHRT finds the accused is unlikely to be fit for trial within 12 months, the ODPP has to decide whether it’s appropriate to continue the case, given the accused’s ongoing mental illness / impairment.

The ODPP will also have to make this decision if:

  • the accused was expected to become fit within 12 months but didn’t
  • at the second fitness inquiry, the judge did not agree with the MHRT that the accused had become fit.

If you are the victim, or a family member of a victim who died as the result of a crime, the ODPP prosecutor will talk you about whether you want the matter to continue, and consult with the police officer in charge, before making a decision. Other factors the we will take into account include the public interest, the seriousness of the offence, the accused’s circumstances and criminal history, the time the accused has already spent in detention, and the likely sentence a court will impose.

Case is discontinued

If, after weighing up all these factors, the ODPP decides not to continue with the case, the accused will be released. The ODPP will notify the victim and the police before this occurs, and will consult with the defence to ensure the accused receives the treatment and care required.

If the ODPP decides to continue prosecuting a case after the accused has been found unfit to be tried, the matter will go to the District or Supreme Court for what is called a ‘special hearing’.
A special hearing is usually before a judge only. It is conducted as closely as possible to a normal criminal trial but the judge can make adjustments to help the accused take part more fully – for example, by having extra breaks if the accused has dementia.

This is the stage at which victims and other witnesses are likely to be called to give evidence. To help you feel prepared, the ODPP prosecutor will arrange to speak with you before the hearing date about your police statement and what to expect on the day. If you have a WAS officer, they will also contact you and can arrange a support person to go to court with you when you give your evidence. (See Going to court and being a witness for information on what will happen before you go to court and on the day.)

The verdicts available in a special hearing are different to those in a normal trial. The accused can be found:

  • not guilty (meaning they are free to go)
  • to have committed an offence, based on the limited evidence available. (The wording of this verdict recognises that the accused may not have been fully capable of giving their version of events to the court)
  • not guilty on the grounds of mental illness.

Diffferent possible outcomes from a special hearing


If the accused is found to have committed an offence, based on the limited evidence available, the judge will impose the same penalty the accused would have received if found guilty in a normal criminal trial. If that would have included prison, the maximum prison term the judge would have imposed becomes the maximum time the accused can be detained anywhere (called a ‘limiting term’.) The judge cannot impose non-parole and parole periods after a special hearing.

The MHRT will then assess the accused and recommend whether they should be detained in a mental health facility for treatment (which the accused has to agree to) or in prison.  The court rarely grants bail while waiting for the MHRT’s assessment if the offence was serious. 

During the limiting term, the MHRT will continue to review the accused. If it finds the accused has become ‘fit’, the ODPP may decide to continue prosecuting the case as a normal criminal matter. If this occurs, another fitness inquiry will take place and, if found ‘fit’, the accused may face a normal criminal trial.

While the ‘limiting term’ is a maximum detention period, if the MHRT finds a person who is due for release remains a risk to themselves or others, it can make them an involuntary mental health patient, or the court can extend the limiting term.

If the accused is found not guilty on the grounds of mental illness after a special hearing, the same process applies as when a court delivers this verdict in a normal criminal trial (see Mental illness / impairment as a defence below).

In NSW, a person must be found ‘not guilty by reason of mental illness’ if a judge or jury believes it is more likely than not that at the time they committed the offence they were:

  • suffering from a mental illness and, because of this
  • did not know that what they were doing was wrong.

Examples of mental illnesses the courts have accepted as a defence include major mental disorders such as schizophrenia, severe mood disorders, and psychosis relating to substance abuse (but not being under the influence of drugs or alcohol).

Mental illness can be raised as a defence in a normal criminal trial, during sentencing or in a special hearing. In every serious criminal matter, the court will ask for reports on the accused from psychiatrists, psychologists or other medical experts, who will often also be called to give evidence.

‘Not guilty by reason of mental illness’ is a verdict victims and other witnesses may find difficult to understand and accept. It can feel like no-one is being held responsible for the harm the crime caused. The NSW Government has recognised this and in June 2018 announced it would change the verdict’s wording. In the meantime, it’s important to know that the verdict is not a finding that the accused did not commit the crime and it doesn’t mean the court doesn’t recognise the harm that has been done.

It’s also important to remember that the verdict can have significant consequences. For example, after a person is found not guilty on mental illness grounds, the court will usually detain them and order that they are assessed by the MHRT. If the MHRT finds they are still a threat to themselves or others, they will remain in detention until this is no longer the case – that is, they will have no minimum or maximum detention period (see Detention for serious crimes involving mental illness or impairment below).

Some defence lawyers avoid using the mental illness defence because of the possibility of indefinite detention, and instead ask the court to take the accused’s mental condition into account during sentencing.

If after a special hearing the MHRT assesses that the accused is no longer a threat, it will usually recommend that they are released with conditions attached, including ongoing treatment and support.

In murder cases, an accused person can be found not guilty of murder but guilty of manslaughter if the court accepts they had ‘substantial impairment by abnormality of mind’ when they committed the offence. This will reduce the maximum penalty they face from life to 25 years in prison.

‘Substantial impairment by abnormality of mind’ is broader than the mental illness defence. For example, it may apply to conditions such as severe depression, brain damage or post-traumatic stress disorder.  It does not include being under the influence of alcohol (although brain damage from long-term drug or alcohol abuse has been accepted as a ‘substantial impairment’).

The accused must show that at the time the offence occurred, their capacity to:

  • understand events
  • judge whether their actions were right or wrong, or
  • control themselves,

was ‘substantially impaired by abnormality of mind’. The impairment has to be from a condition they already had and substantial enough to reduce murder to manslaughter. 


  • Diagram of complete legal process for serious crimes involving mental illness or incapacity.