A justice lobby group says too many people are being acquitted of crimes on mental health grounds.
The Sensible Sentencing Trust has obtained figures under the Official Information Act which show a nearly seven-fold increase between 2000 and 2012 in not-guilty verdicts by reason of insanity.
Spokesperson for the trust, Ruth Money, told Radio New Zealand's Nine to Noon those who have been found not fit to plead to a charge should still be tried and convicted through the criminal justice system.
Ms Money says people committing such crimes are not getting proper mental health treatment and a public discussion is needed on how the law is applied to them.
Crown Prosecutor Simon Moore says it could be possible to introduce a verdict which finds a mentally impaired person guilty of a crime.
Mr Moore says there may be a way to do that, but mentally ill people cannot be put into the same category as homicidal criminals.
