Highly trained and experienced war veteran Ben Roberts-Smith allegedly lost control and kicked an unarmed Afghan man off a cliff because he laughed at him.
In the second and final week of defamation trial closing submissions on Monday, barrister Arthur Moses SC said the Federal Court was asked to find his client's motivation for the allegation was "this man laughed at Mr Roberts-Smith twice".
"That a trained Australian soldier of the calibre of Mr Roberts-Smith and his undisputed record would so impulsively and cruelly first assault and then order the execution of an unarmed civilian in response of the slightest provocations is inherently improbable," Mr Moses said.
The Victoria Cross recipient is suing The Age, The Sydney Morning Herald and The Canberra Times over 2018 reports claiming he committed war crimes in Afghanistan including murder, and acts of bullying and domestic violence.
The 43-year-old denies all claims of wrongdoing, while the newspapers are defending them as true.
He is accused of kicking an innocent farmer called Ali Jan off the cliff and down into a river bed in September 2012 at Darwan.
The handcuffed prisoner was allegedly shot by another soldier, both alleged to be working in a joint criminal enterprise to carry out the murder.
Afghan eyewitnesses to the event were found through a middleman "fortuitously as luck would have it," and then set up with the mastheads who paid their rent, food and medical expenses for more than a year so they could give the evidence via videolink from Kabul, Mr Moses said.
"One cannot rule out the possibility this may have influenced their evidence."
He also pointed to another witness dubbed Person Seven, saying he was so obsessed that Mr Roberts-Smith was awarded the prestigious and rare medal that he sought to destroy his reputation using the media.
"To do all that he can to throw mud at (Mr Roberts-Smith) ... and engaged in a war of words ... in the dark and through the media.
"Person Seven heard rumours ... and because of the Victoria Cross he starts hunting for war crimes."
The barrister submitted another former SAS soldier dubbed Person 14 lied to the court about a story that "flip-flopped" on numerous occasions.
"The lies drip from this man's evidence," Mr Moses said.
Person 14 testified that he observed a soldier wearing Mr Roberts-Smith's distinctive camouflage paint carrying his automatic Minimi weapon on a mission to a Taliban compound dubbed Whiskey 108 in 2009.
He said the soldier threw a figure to the ground before unloading an extended burst of Minimi fire upon them.
The barrister said notes from journalist Chris Masters dated February 2018 about his meeting with Person 14 stated that it was another soldier who shot the prisoner with a fake leg.
"But he told Your Honour that he told Mr Masters that it was Mr Roberts-Smith who shot the man with a prosthetic leg," Mr Moses said.
"He never told Mr Masters that, that would have been red hot for Mr Masters, he would have been tripping over himself to get to the editor's room.
"He contorted and twisted himself until the stage of lacking any credibility at all by the time he left the witness box."
Person 14 also told the court he saw Mr Roberts-Smith order Afghan soldiers to shoot a detained local man "or I will" during a 2012 mission in Khaz Uruzgan, something he denies.
Barrister Nicholas Owens SC on behalf of the newspapers last week said Mr Roberts-Smith colluded with several of his witnesses and good friends through clandestine meetings and swapping of evidence, and showed a guilty conscience of war crimes.
The trial is expected to resume in closed court on Tuesday.
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