Belief a man who's killed a second time after being found insane after a killing more than two decades ago -- shouldn't have been let out of the forensic unit

RNZ's revealed the man was recently found not guilty of murder by way of insanity again -- as he'd believed the victim was possessed.

He'd been a special patient under the Mental Health Act but released more than 10 years ago.

The Government's chief victims adviser says Ruth Money says -- she'd like to see a Royal Commission into how we're assessing people to ensure they won't reoffend.

She says it's not good enough people are going on to kill -- it's too dangerous for the community and there needs to be a level of inquiry that has teeth.