Matthew Spencer, 27, was on Thursday ordered by Supreme Court Acting Justice Peter Hidden to be detained until he is deemed fit to be released into society.

Spencer admitted stabbing his father, Shane Spencer, in the head, neck, chest, back and arms with a serrated-edge steak knife inside their home at Trundle, near Parkes, in September 2018.

While he was deemed fit to stand trial, his lawyers argued he should be found not guilty by reason of mental illness, a submission which crown prosecutor Liam Shaw agreed with.

Acting Justice Hidden found Spencer - a diagnosed schizophrenic - should be detained until a court rules he no longer represents a danger to the public.

One forensic psychiatrist's report tendered to the court said, at the time of the killing, the accused was "labouring under such a defect of reason arising from a disease of the mind that he did not know the nature and quality of the act he was committing".

The report found Spencer "did not know that it was wrong".

Spencer had regularly been admitted for treatment for "psychosis-based religious delusions" between 2016 and 2019.

He also "exhibited paranoid religious ideation in relation to being Jesus, Lucifer and the devil" in the months before he left his father to die in a pool of blood.

His mental illness was likely exacerbated by years of substance abuse and use of amphetamines, the court heard.

Immediately after the incident, he made a series of bizarre social media posts including: "Trust God. It's written in the stars. No satellites can change it. I'm sorry once again. But I gotta show no love. Love will get you killed."

He went to the nearby Trundle Hotel where he drank and smoked and was seen with blood on his face and clothes.

He then used the Trundle Police Station's phone to call officers to tell them he had stabbed his father - claiming he was spurred on by US rapper Jay Z.

"Gangsta rap made me do it. The Jay Z Encore, the song that made me do it," he told them.

Australian Associated Press