Stephen Staff spent five hours in the home of Matthew Davis after bashing the frail 31-year-old to death in an attempt to conceal the motive behind his killing, prosecutors allege.
Staff is facing a murder trial which began in the NSW Supreme Court at Wollongong on Monday.
The court heard Mr Davis suffered serious facial injuries and choking, some combination of which caused his death on August 21, 2021 at his Lake Illawarra home.
Mr Davis' mother told the court her son was in very frail health at the time of his death, suffering from chronic asthma among other serious conditions, making him "too sickly to work".
CCTV footage viewed by the court showed three men heading in the direction of Davis' house that night and just two of the men returning about15 minutes later.
In the footage, it takes the third man around five hours to be seen again, carrying what appears to be a plastic bag filled with heavy items.
Prosecutors allege that man is Staff, and in the bag are Mr Davis' mobile phone, laptop, gaming console and modem, which were removed from the home.
While prosecutors told the 13-person jury the reason for the attack is not clear, they heard Davis struggled with gambling addiction, mostly for football and online poker, and may have had unpaid debts at the time of his death.
The court also heard while Staff initially denied being at the home to police, he later told family members in recorded calls from prison that effectively Mr Davis had a debt and the men were there to "give him a touch up".
Staff's lawyer told the court while he had initially lied to police about not being present, the truth is he was there but did not take part in the fatal bashing.
The court heard Staff's DNA was found by police at the crime scene and on Mr Davis' body because he had tried to help him afterwards.
Prosecutors argued Staff's DNA was present because he actively took part in the bashing which claimed Mr Davis' life.
"It is the crown case that Mr Staff, together with the two other men, assaulted Mr Davis," the crown prosecutor said.
"Mr Staff's DNA is on Mr Davis' hood because he was holding or handling Mr Davis by his hood around his neck area."
Mr Davis' mother and grandmother, with whom he was very close, both appeared as witnesses on day one of the trial.
Both women said they had been asked on a number of occasions by Mr Davis to borrow money which they understood to be to pay off gambling debts.
Before his death Mr Davis had asked to borrow around $900 which Ms Davis said she had on hand and had agreed to give him, but that her grandson had never come to collect.
"I just assumed that he had gambled and won that money back," she told the court.
