There's belief a man who killed a second time after being found insane after a killing more than two decades ago shouldn't have been released. 

RNZ has 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 was freed more than 10 years ago. 

The Government's Chief Victims Advisor, Ruth Money, say she'd like a Royal Commission inquiry of how people are assessed to ensure they won't reoffend. 

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

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