Read more:
• Churchis murder accused 'went overboard' - witness
They said a dispute arose because Mr Linder had been "going to the toilet" in a spot on Mills Lane where they were planning to sleep that night.
It also appeared the man had interfered with their property, they said.
When Churchis - known to his friends as 'DJ' - and a young woman returned from a nearby fast food restaurant Churchis came upon them arguing with Mr Linder, the court was told.
As the victim tried to leave, Churchis kicked him in the chest, sending his head crashing onto the concrete underneath him, the witness said.
Churchis then "went overboard" and allegedly began punching him, which was when the witnesses walked away.
"He just started stomping on his face ... all I could see was him standing up and kicking."
The man told the court he later poured a bottle or urine over Mr Linder.
Another of Churchis' friends told the court that they didn't ring an ambulance because they didn't realise how seriously injured Mr Linder was.
A doctor who treated Mr Linder gave evidence that his prognosis was "very poor" when he was admitted to intensive care.
"We could not say he had any chance of making a good survival," Dr Craig Hourigan of the department of critical care told the trial.
Mr Linder suffered severe brain and facial injuries and, combined with a previous head injury he suffered in 2001, it was unlikely he would live, he said.
Rather than aggressively treat his injuries, Mr Linder's family asked doctors to administer pain medication until he passed away.
The jury, which retired yesterday, will continue deliberations today.
Read more: Homeless man murder: Accused seen high-fiving mates