A young man knew he intended to kill his best friend before bashing him to death after overdosing on MDMA and in a drug-induced psychosis, a Sydney jury has heard.
After smoking up to 20 cones of cannabis and taking about his 10th and final MDMA capsule, Mathew Flame was so drug-affected his mind-altered state believed Liam Anderson was a demon or possessed, crown prosecutor Gareth Christofi said in his closing address on Thursday.
"Not saying he walked off and a devil and demon with a tail and horns appeared... a fantastic creature he intended to kill," he said.
The Crown submits that Flame knew very well his best mate Mr Anderson had been with him, saying "I'm always going to be here man, I'm never going to leave you".
"He was just there....typical Liam... always caring about me and s***," Flame later said during an interview.
Flame's own words show he knew Mr Anderson was the person he intended to kill or cause serious harm to, the prosecutor argued in the NSW Supreme Court.
Flame, a 22-year-old apprentice plumber, pleaded not guilty by reason of mental impairment to murdering the son of Angry Anderson, singer with hard rock band Rose Tattoo.
Liam Anderson was last seen alive on November 4, 2018 in a Queenscliff park on Sydney's northern beaches, after the friends had partied at the Burdekin Hotel together during the night.
An American tourist earlier testified he saw Flame stomping repeatedly on the bloodied head of his mate who was yelling out for help, before he called triple-zero shortly after sunrise.
A major issue of the trial is whether Flame was suffering from a disease of the mind in the form of schizophrenia at the time of the murder.
Forensic psychiatrist David Greenberg had told the court Flame was suffering from a drug-induced psychosis and there was no evidence of a pre-existing mental illness which he was diagnosed with more than seven weeks after his arrest.
The psychosis appeared to come and go with the effects of the drugs and went hand in hand with his intoxicated state, Mr Christofi said.
Another forensic psychiatrist earlier told the court that it was possible he was already experiencing precursor symptoms of schizophrenia, the signs of which may have been missed.
But Professor Greenberg argued one "can't retrospectively re-engineer the medical evidence to say someone had schizophrenia at the time".
NSW Police forensic pharmacologist and toxicologist Shuang Fu concluded that Flame's blood sample showed the amount of MDMA in his system during the murder was likely within the "toxic range" which can cause "induced psychosis with auditory and visual hallucinations or delusions".
Mr Christofi conceded this was a "very sad and tragic case from whatever angle one chooses to look at it".
The Crown's closing remarks continue before Justice Richard Button.