A jury has begun deliberating at the trial of Mathew Flame, who's accused of the bashing murder of his best friend while believing he was a demon trying to hurt him.
The 22-year-old apprentice plumber pleaded not guilty by reason of mental impairment to murdering Liam Anderson, son of Angry Anderson, singer with hard rock band Rose Tattoo.
Flame repeatedly stomped on Mr Anderson shortly after sunrise on November 4, 2018 in a Queenscliff park on Sydney's northern beaches.
The prosecution contends Flame was psychotic at the time due to his voluntary use of drugs including ecstasy, while the defence says he was labouring under the severe mental illness of schizophrenia.
Crown witness Professor David Greenberg said in his opinion Flame was in a drug-induced psychosis and did not have a disease of the mind when he attacked his mate.
While he believes Flame now qualifies for a diagnosis of schizophrenia, he said such a disorder developed more than seven weeks after he was taken into custody.
But another forensic psychiatrist Dr Kerri Eagle, called by the defence, said she believed Flame had the underlying condition of schizophrenia at the time of the killing.
She said he has had subsequent psychotic episodes of a similar nature while on remand and has since developed a severe form of the disease that has been resistant to treatment.
After Justice Richard Button completed his legal directions, the NSW Supreme Court jury retired on Monday afternoon to consider its verdict.