Australian troops in Afghanistan killed a man with a prosthetic leg, which was then taken as a souvenir and brought back to Perth to be used as a novelty beer drinking vessel.

The incident is one of several involving a rogue Special Air Service Regiment team which has been uncovered by a Fairfax Media investigation and corroborated by special forces insiders.

On the same mission in 2009, a trooper on his first deployment to Afghanistan was pressured to execute an elderly, unarmed detainee by fellow higher-ranking soldiers as part of a "blooding" ritual, according to defence insiders who were witnesses at the scene.

SUPPLIED A prosthetic leg was used as a novelty drinking vessel by Australian soldiers. It's one of a raft of incidents under investigation.

The grey-haired, bearded Afghan man executed by the "rookie" was, according to some SASR members, a suspected Taliban member, but at the time presented no threat to Australian soldiers.

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The newly deployed soldier allegedly shot the man after being prompted by two more senior soldiers, one of whom was earlier overheard proclaiming a need to "blood the rookie".

One of the sources said the killing was less abhorrent than the pressuring.

"If shit needs to be done, do it yourself," the soldier said.

SASR sources claim the man with the prosthetic leg was machine-gunned by a soldier that, for legal reasons, Fairfax Media will call "Leonidas".

Leonidas is also implicated in the killing of a detainee three years later in September 2012 during a SASR mission in the village of Darwan.

Leonidas allegedly kicked handcuffed detainee Ali Jan off the edge of a small cliff, badly injuring his face, according to claims of two defence force insiders who witnessed the event.

As the detainee lay injured, hands still bound, the two witnesses say Leonidas was party to the decision among soldiers to "get him out of his misery".

The claims have been backed by the relatives of Ali Jan who were interviewed this week by an Afghan journalist on assignment with Fairfax Media.

The allegations, which have circulated among insiders for years, have now been corroborated by various sources across the globe during a six-month investigation.

Observers say as the war bled on, Australian special forces operators engaged in too many deployments and became desensitised. Over time, the secretive status of special forces generated a culture allowing mateship to overwhelm accountability.

In a statement, the Australian Defence Force said an ongoing inquiry by its Inspector-General, assisted by NSW Supreme Court judge Paul Brereton, would make "recommendations" about how to deal with any substantiated allegations of war crimes.

"The IGADF Afghanistan Inquiry has, for some time, been aware of allegations of significant issues involving the Special Operations Task Group in Afghanistan, which are within the scope of the Inquiry," the statement said.