An apprentice plumber who believed his best mate was a demon when he fatally bashed him was in a drug-induced psychosis at the time, a forensic psychiatrist has told a jury.
Professor David Greenberg said in his opinion Mathew Flame did not have a disease of the mind when he attacked Liam Anderson, son of Angry Anderson, singer with hard rock band Rose Tattoo.
Prof Greenberg was giving evidence for the Crown in the NSW Supreme Court on Thursday.
Flame, 22, has pleaded not guilty to murdering Mr Anderson by repeatedly stomping on him 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 including ecstasy, while the defence says he was labouring under the severe mental illness of schizophrenia.
Prof Greenberg interviewed Flame in January 2020 and considered material including police videos of him after his arrest and medical records from when he went into custody.
"At the time of the alleged offence I am of the opinion he was suffering from a drug-induced psychosis," he said.
Prosecutor Gareth Christofi asked: "In a drug-induced psychosis are the taking of the drugs the necessary ingredient - if your remove the drugs do you get a psychosis?"
"No," the witness replied.
He said there was no evidence of Flame having a pre-existing or current mental illness which was triggered or aggravated by his drug use at that time.
While Prof Greenberg 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.
He couldn't exclude the possibility Flame had re-experienced the trauma of when he saw the demons and believed Mr Anderson was going to attack him as part of PTSD.
Up until the bashing, Flame was by all accounts a healthy, functioning young man who had a group of friends, was working and interested in body building.
"For all intents and purposes he had no symptoms or signs of having a mental illness," Prof Greenberg said.
"'Obviously he was using illicit substances prior to 3 November 2018.
"But aside from his drug use, he appeared relatively normal in all these aspects of looking at him."
The police videos showed him coherent and developing insight into what he had done in a relatively short time after the psychosis, while schizophrenia symptoms could continue for days or weeks or longer.
Flame told the psychiatrist that about four months before the bashing he had a night of drinking and consumed eight capsules of MDMA.
"For only a few minutes" when he got to a construction site he thought his workmates were demons and "felt scared and anxious so walked away and drove home".
Prof Greenberg said "if this occurred" the fact it lasted only a few minutes was more in keeping with a combination of intoxication and MDMA withdrawal.
The trial continues before Justice Richard Button.
Australian Associated Press
