A man accused of a "drunken, brutal" killing on a small island off Queensland's south-east coast told an undercover police officer he "got stuck into" a man after finding him in bed with his girlfriend, a jury has heard.
On Monday, Paul Anthony Quinlan pleaded not guilty to the murder of Scott Pilton on Lamb Island in May 2020.
The 48-year-old was unconscious when he was taken to hospital and died two days later of a brain bleed.
Crown Prosecutor Michael Lehane told the jury Mr Pilton had been drinking with Mr Quinlan and Mr Quinlan's partner at her house before he was assaulted in "one or perhaps more drunken brutal attacks".
"[Mr Pilton] left the house in an ambulance destined to die," he said.
Mr Lehane told the jury they would hear evidence "there was no acts of physical aggression on [Mr Pilton's] part".
"Mr Pilton did not hit, slap, punch or even lay a finger … upon [Mr Quinlan]," he said.
"The accused simply beat him, in what the crown says, effectively to death."
Mr Lehane told the court that after being arrested, Mr Quinlan confided in an undercover police officer in the Brisbane Watch House.
Parts of that recorded conversation were read out to the jury during the opening address, which included Mr Quinlan describing how he "got stuck into someone".
The jury heard Mr Quinlan told the officer he had left the home where the trio had been drinking and when he returned, found Mr Pilton naked and asleep in his partner's bed.
"So he copped a flogging — he was knocked out," Mr Lehane said Mr Quinlan told the officer.
"He was asleep in the bed, I just dragged him out."
Mr Quinlan also told the officer "I lost my shit" because Mr Pilton had said to him "either you leave or me", the jury heard.
Mr Quinlan's lawyer, Tim Ryan, told the jury his client had repeatedly punched Mr Scott while in an "intoxicated and emotionally heightened" state but they would have to determine "two primary factual issues" in order to find him guilty of murder.
This included how Mr Scott suffered the fatal haemorrhage, and if it was caused by the punches, "whether in that moment … did [Mr Quinlan] have intention" to kill or do grievous bodily harm to him.
The trial continues.