This document mentioned the deaths of nine enemies killed in action including two "squirters" - military speak for insurgents attempting to flee a battlefield - and did not refer to any prisoners being captured on the day of the April 2009 event.

In June, Federal Court judge Anthony Besanko found Mr Roberts-Smith was involved in four unlawful murders, including two at Whiskey 108 involving insurgents who emerged from a secret tunnel located in the compound.

The judge found Mr Roberts-Smith ordered the execution of one insurgent to "blood the rookie" and machine-gunned another by himself, stealing his prosthetic leg for use as a novelty beer drinking vessel.

The 2600-paragraph decision was a comprehensive loss for the Victoria Cross recipient in his defamation case over 2018 reports in Nine-owned papers The Age and The Sydney Morning Herald, plus The Canberra Times.

Mr Roberts-Smith has always denied being involved in any unlawful killings and has not been criminally charged.

Mr Walker told the Full Court there was no explanation as to why the judge had preferred witness testimony based on memories of events 13 years ago over documents created closer in time to the event.

Nowhere had Justice Besanko explained how he found the patrol debrief had been "nefariously corrupted" to cover up the murders, the barrister told three appeal judges and a packed courtroom.

While the judge had found eye-witnesses to the claimed murders had no motive to lie, there was no onus on Mr Roberts-Smith to prove this motive in court, Mr Walker said.

This led Justice Besanko to err, he argued.

“You can't dismiss evidence simply because you think other evidence is correct."

Differences in testimony between those at Whiskey 108, including whether only one person or two emerged from the tunnel, were not adequately explained by the judge and were "shrugged aside", the court heard.

"Nothing is supplied so as to distinguish in any way at all between the reliability of different versions by different people all supposedly in the same place," Mr Walker said.

How the alleged murders were meant to have occurred was implausible, the court was told.

Not only was the blooding of the rookie said to have occurred in a deserted courtyard in a compound teeming with people, but Mr Roberts-Smith was alleged to have asked to borrow a suppressor despite carrying one himself.

“One's completely lost contact with any foundation in fact based on evidence," Mr Walker said.

The barrister argued that Justice Besanko erred by failing to give enough weight to Mr Roberts-Smith's presumption of innocence when delivering his judgment.

The 10-day appeal challenges further findings from June, including that the decorated soldier kicked a handcuffed prisoner off a cliff near the village of Darwan and ordered him executed.

He is also challenging a finding that he ordered the execution of an Afghan man being questioned in the village of Chinartu after a cache of weapons was found hidden in a wall cavity.

In his decision, Justice Besanko found Mr Roberts-Smith bullied fellow soldiers to prevent them from speaking out about his actions, threatened witnesses and hired private investigators to track them.

If the legal challenge is unsuccessful, Mr Roberts-Smith and his financiers at the Seven Network - including billionaire Kerry Stokes - will be on the hook for tens of millions of dollars in legal costs.

The hearing continues on Tuesday.

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