Vic murder witness afraid of being killed

A man who helped dump the body of a 33-year-old Victorian woman has told a court he went along with it because he didn't want to end up dead too.

Wayne Marmo, who shot Simone Quinlan in the head five times before dumping her body in a mine shaft at Kangaroo Flat, pouring petrol on her and setting her on fire, is on trial for her murder.

But his defence team claims Ms Quinlan was already dead when he shot her after she was violently assaulted by her boyfriend, Brendan Neil, at Melton in August 2015.

Marmo's defence lawyer Scott Johns has argued his client was instead guilty of attempted murder.

A witness who can only be identified as DJ, said he saw Neil hitting Ms Quinlan in the head with a hammer and wrapping her face with black duct tape.

He said he was fearful "for my own safety" and that Neil had threatened him not to say anything about what had transpired.

"Pretty much, (he said) keep your mouth shut or the same thing will happen to you and your family," he told the Supreme Court of Victoria on Monday

DJ said Neil's assault on Ms Quinlan went from "bad to worse", from verbal arguing, to punching and kicking, to four or five blows to her head with a hammer.

He said at that point, "massive pools" of blood began collecting on the floor around Ms Quinlan and that she "appeared lifeless".

DJ said he then accompanied Marmo in his Hilux to dump the body, which Neil had wrapped in a blanket and stored in the ute's tray under a tarp.

He said he went along with things because he "didn't want to end up like Simone".

He said the car's occupants thought they saw the tarp moving but DJ put it down the the wind, believing Ms Quinlan was already dead.

Marmo then shot her in the head in bushland at Bacchus Marsh.

A forensic anthropologist earlier told the court it was impossible to know whether Ms Quinlan was already dead at the time of the shooting.

Soren Blau told the court the gunshot wounds occurred perimortem, that is, around the time, shortly before or shortly after death.

Dr Blau told the court Ms Quinlan's head, torso, and pelvis and leg were recovered in three separate parts.