What does it mean when a person charged with murder is found not guilty by reason of insanity?

Who decides that they are insane and what proof is needed in court?

What happens to them after that - are they allowed to walk free like others found not guilty of a crime?

Here we explain insanity in the context of the New Zealand justice system.


What is the legal definition of insanity?

In New Zealand law insanity has a very strict legal definition.

To be held criminally responsible a defendant must be physically and mentally culpable of an offence.

Legally this means that, as well as establishing that the defendant actually committed the crime, it has to be established that they had a "guilty mind".

However, if they were so mentally disordered that they did not know what they were doing, or they were not capable of understanding that their actions were morally wrong, the defendant can be deemed "legally insane".

Who decides if a person is legally insane?

Only a judge can make that decision, after hearing from multiple forensic psychiatric experts.

Before 2003 a defendant could be found not guilty by reason of insanity at the conclusion of a trial.


Changes to the Criminal Procedure (Mentally Impaired Persons) Act 2003 mean that if both the defendant's lawyer and Crown solicitors agree, and if the judge is satisfied by expert evidence that the person was legally insane they can be found not guilty by reason of insanity without any need for a trial.

What happens after a person is found not guilty by reason of insanity?

In most New Zealand cases if someone is acquitted of a crime on insanity grounds the presiding judge makes an order that they are detained as a special patient.

They remain a special patient detained at a forensic mental health facility until the Minister of Health or the national Director of Mental Health deem they are no longer a risk to themselves or others.

The defendant may be released sooner than if they had been convicted of the crime they were charged with, or may remain a special patient for much longer than the maximum prison sentence would have been.

Does a person found not guilty by reason of insanity have a criminal record for that crime?

No. They are not found guilty so therefore not convicted.