War veteran Ben Roberts-Smith allegedly kicked an unarmed and handcuffed Afghan prisoner, "catapulting" him over a cliff, before telling his squadmates a "story" to cover up the execution.
But the witness who made this allegation in the Federal Court may not be forced to give evidence about an alleged murder he perpetrated for fear of criminal prosecution.
The former SAS sergeant, codenamed Person Four, told the court on Monday about a controversial mission during which local man Ali Jan was allegedly handcuffed and kicked off a "steep slope" in the village of Darwan, Uruzgan province in September 2012.
The witness said the man with a donkey carrying wood was searched and handcuffed before the troop's "extraction" was radioed in, prompting their removal to another location.
Person Four said he rounded the corner of a rocky slope and spotted another soldier holding the same prisoner with his "back towards a large drop-off," he said.
Person Four was "trying to understand what was happening" as he noticed Mr Roberts-Smith positioned a few metres away.
"He turned around, walked forward (and) kicked the individual in the chest.
"The individual was catapulted backwards and fell down the slope."
Person Four said he could see the prisoner's face strike a large rock and sustain a "serious injury".
"Your Honour it knocked out a number of his teeth including his front teeth."
Mr Roberts-Smith vehemently disputes the allegations and has previously testified the man was a Taliban spotter shot in a cornfield.
The 43-year-old war veteran is suing The Age, The Sydney Morning Herald and The Canberra Times for defamation over reports that he committed war crimes and murders in Afghanistan between 2006 and 2012.
Person Four described being "in some shock" when he followed soldiers to a creek bed.
As the troop approached the man he "attempted to sit up and fell back down again," and Person Four said he and another soldier were ordered to drag him over to a large tree.
After walking some distance away he turned around to see the prisoner standing before "shots rang out".
A "fogged up" Icom radio with a wet screen, he believed Mr Roberts-Smith had retrieved from another dead insurgent across the river, was then allegedly placed on the body for photographs.
It followed previous advice Mr Roberts-Smith allegedly gave him "that we needed to carry items on our equipment to validate engagements".
After the mission the decorated soldier debriefed with a number of commanders before he rejoined his three troop comrades in another room, Person Four said.
He then alleged Mr Roberts-Smith said words to the effect: "This is what the story is. The story is that we engaged a spotter."
As a trooper on his first deployment to Afghanistan in 2009 Person Four was allegedly ordered to execute an older prisoner near a Taliban compound nicknamed Whiskey 108.
But on Monday Person Four became the first witness to decline answering questions by Nicholas Owens SC on behalf of the media outlets, even with the protection of court-ordered immunity.
Mr Owens later conceded while he wished to hear the evidence he did not seek to further compel the former special forces soldier due to the risk of prosecution by the International Criminal Court.
Instead, he would rely on the "significant body of evidence" that allegedly incriminates Person Four, Mr Owens said.
Person Four also recounted a whiteboard with a drawing depicting a "winged penis kicking an individual" from a cliff, saying Person 35 had a reputation for winged penis cartoons.
Mr Roberts-Smith - one of a handful of Australian recipients of the Victoria Cross since 1970 - has suggested the execution claims and others stem from jealous associates spiteful of his medallic achievements.
The trial continues.
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