"It seems to be agreed that there was a deficit of reason in the form of psychosis," Justice Richard Button told the NSW Supreme Court jury on Friday.

He was giving the jurors legal directions before the Crown case resumes on Monday.

Justice Button previously warned them to disregard any feeling of prejudice or sympathy, describing the case as a "very sad story from every perspective".

Mathew Flame, 22, has pleaded not guilty by reason of mental impairment to the bashing murder of Mr Anderson, the son of Angry Anderson, the lead singer of hard rock band Rose Tattoo.

An American tourist has testified to seeing an emotionless assailant repeatedly stomping on the bloodied head of his victim shortly after sunrise on November 4, 2018, in a Queenscliff park on Sydney's northern beaches.

The Crown contends Flame was psychotic at the time due to his voluntary use of drugs, while the defence says he was labouring under the severe mental illness of schizophrenia.

Justice Button gave the jurors directions about the defence of mental illness.

"Apart from anything else, it seems to be agreed the accused believed not only that the deceased was trying to harm him, but also indeed that the deceased was a demon," he said.

"But has it been proven, on balance, that that arose from a disease of the mind from which the accused was suffering from on the morning of 4 November, as the defence contends?"

Or did it arise, as the Crown maintained, from the mixture of alcohol, cannabis and a very large quantity of MDMA upon a mind which was otherwise healthy, the judge said.

The jury has been told that after his arrest, Flame constantly rambled about Satan before telling police "I was possessed last night" and "my mate actually had the demon inside him".

On Friday, the jury was shown videos of Flame taken hours later, before he underwent forensic procedures, when the detective involved described him as being calm and co-operative.

The trial resumes on Monday.

Australian Associated Press