Barry Paul Cavanagh and Nathan McIvor, both 38, and Sean David O'Keefe, 39, have pleaded not guilty to murdering Jamie Phillips in October 2018.

The 46-year-old's naked body was found in a vacant Campbelltown lot on October 25, 2018.

McIvor's then-partner Amanda Robinson told the Supreme Court trial on Wednesday about seeing her partner looking scared and worried following the incident.

McIvor tried to perform CPR on Phillips after he "dropped to the ground" but someone said it was too late as he had been stabbed, she said.

He told her someone had died following a fight with his mates and that he had to get rid of the body and evidence.

"Nathan was scared of his co-eys and what was going to happen if we didn't get rid of the stuff," she said, referring to his co-accused.

"He said his co-ey had said to him either you're in or you're out."

"If he didn't get rid of the stuff it could cause his family to be in danger."

The pair picked up a big metal drum from her sister's before taking it to a deserted bush trail and burning a number of items in it using petrol.

She later became upset with McIvor when she saw on television news that the body was left wrapped in plastic and unclothed.

The Crown argues the men acted in a joint criminal enterprise to cause grievous bodily harm to Mr Phillips through a "sustained or prolonged physical assault" that led to Cavanagh pulling out the knife that ultimately killed the victim, the Crown submits.

But O'Keefe's lawyer Richard Pontello SC submits his client was the one who stabbed Mr Phillips in self-defence.

The trial continues.

Australian Associated Press