Mentally ill NSW man not guilty of murder

When a mentally-ill NSW man who thought he was a character in a Stephen King horror-film heard the devil tell him to "kill, kill, kill" he picked up his room mate's guitar and bashed his head in.

Paul Hindmarsh then used the electric guitar's lead to strangle Joseph Gumley, 47, at a high-dependency psychiatric ward at Shoalhaven in which he had been involuntarily living for 11 months.

But when Hindmarsh noticed his victim was still breathing, he swung the guitar back into his head, leaving him with fatal injuries ward staff would discover on the morning of July 31, 2014.

Hindmarsh was subsequently charged with murder but was on Friday found not guilty by way of mental illness, following a brief hearing in the NSW Supreme Court in Sydney.

The court heard Hindmarsh had been diagnosed with schizophrenia in 2004 and had intermittently been forced to reside in psychiatric wards.

He returned to the Shoalhaven hospital in August 2013.

Eleven months later when orderlies were waking people for breakfast they noticed a chocolate-coloured spatter near Mr Gumley's head, which was under a cloth.

It had been covered by Hindmarsh, who earlier that morning had turned on his room mate.

Hindmarsh, the court heard, had been awake most of the night before.

The devil had been telling him to "kill, kill, kill" and he believed he was the character Jack from the horror-film The Shining before he attacked Mr Gumley sometime between 6.30am and 7am.

Two forensic psychologist reports tendered to the court both said Hindmarsh suffered from chronic, untreatable schizophrenia.

Justice Stephen Campbell accepted their finding that while Hindmarsh was aware of his actions, he couldn't determine their wrongfulness due to "thought-process problems".

"Mr Hindmarsh wasn't able to distinguish between reality and his hallucinations," Justice Campbell told the court.

"He didn't know what he was doing was wrong to the standards of an ordinary member of the community."

While Hindmarsh was found not guilty of murder, it will be a long time before he's released from custody.

He will remain in a jail or hospital under supervision and his case will be reviewed every six months by a judge and also at other times by a mental health tribunal.

He will remain in custody until he is considered to not be at risk of causing harm to anyone, the court heard.