Ben Roberts-Smith's good friend has denied colluding with the decorated soldier and others via email exchanges to collaborate about alleged war crimes.
The former SAS soldier codenamed Person 29 began his evidence in the Federal Court on Wednesday about a 2009 mission to a Taliban compound dubbed Whiskey 108 in Uruzgan province.
He previously backed up the Victoria Cross recipient's claim that "no men" were found there inside a secret tunnel, a controversial detail that has become crucial in the court case.
Mr Roberts-Smith is suing for defamation The Age, The Sydney Morning Herald over 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 mastheads are defending them as true.
The former SAS corporal is allegedly responsible for six unlawful deaths during his deployments in Afghanistan, two of which are said to be unarmed prisoners found inside the tunnel at Whiskey 108.
A young trooper was allegedly ordered to execute one of the prisoners who surrendered willingly, according to one soldier's testimony, while Mr Roberts-Smith is accused of publicly executing the other.
He denies all claims of wrongdoing and said both were insurgents lawfully killed within the rules of engagement.
On Thursday Person 29, the godfather to one of Mr Roberts-Smith's children, denied trying to harmonise their accounts together to cover up the alleged war crimes.
"This email represented a collaboration between the two of you about key details regarding Whiskey 108," the media outlets' barrister Nicholas Owens SC asked Person 29.
"That's not correct," he replied.
He said he deleted the email out of habit, and not because it contained anything incriminating.
Mr Owens submitted that Person 29 met for dinner with other SAS soldiers prepared to lie about their evidence to the Inspector-General of the Australian Defence Force, but he denied this.
The former SAS patrol commander also denied trading notes with Mr Roberts-Smith about his interviews with the IGADF.
However, he did recall sitting down to dinner with one of the other key witnesses the night his IGADF interview had finished.
When media articles first aired the allegations, Person 29 said he was "angry, frustrated, dismayed and disappointed," and that he felt betrayed by comrades speaking to journalists.
"If that's their recollection I can't stop that, but Your Honour, even though this is a defamation case, this is the forum to arbitrate and air those concerns," he said.
"Not by speaking to the media, not in the court of public opinion."
The trial before Justice Anthony Besanko continues on Friday.
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