The Brereton probe was launched after a report in March 2016 by then Special Operations Commander Major-General Jeff Sengelman identified serious "governance and behavioural lapses" within the SAS. The establishment of the Brereton probe was supported by senior Defence officials including Defence Force chief Lieutenant-General Angus Campbell and has the backing of former SAS officer turned MP Andrew Hastie, the Australian Defence Association and, privately, many SAS soldiers. But the investigation of anything but the most "egregious" war crimes has been attacked by War Memorial head Brendan Nelson. Some ex-soldiers, including Mr Roberts-Smith, have also attacked the inquiry, claiming it is chasing "rumours". War Memorial head Brendan Nelson and SAS veteran Ben Roberts-Smith. Credit:Katherine Griffiths Mr Roberts-Smith, a Victoria Cross recipient for acts of bravery in Afghanistan, is one of a small number of soldiers being probed by the Brereton inquiry. Special forces insiders have implicated small SAS teams Mr Roberts-Smith helped to lead in alleged serious breaches of the laws of armed conflict. He denies all wrongdoing and has vowed to expose the allegations as lies while suing Fairfax Media over a report that detailed the claims.

In June, Fairfax Media reported a key inquiry witness and member of the SAS was sent a letter threatening retaliation if he did not recant his testimony to the inquiry. Sources familiar with the contents of the first letter said it included detailed references to the activities of 2 Squadron SAS and was designed to scare the witness, an experienced soldier, into covering up information being sought by the Brereton Inquiry. It has now emerged that a second letter was sent after the reports of the first threat were published. The second threat also arrived in the form of anonymous letter sent to a confidential post box used by the SAS in Perth. Defence Force chief Lieutenant-General Angus Campbell. Credit:Alex Ellinghausen The sender identified himself as a “friend of the regiment”, according to a source. The second threat was sent within days of the recipient, a patrol commander, alerting defence officials that he had received the original letter containing threats.

The letters contain details about the activities of some members of patrols that Mr Roberts-Smith was a part of between 2009 and 2011, according to a source. There is no suggestion that Mr Roberts-Smith is involved in sending the letters. However, the federal police and defence investigators are examining if the mystery perpetrator was seeking to stop allegations being made about the high profile soldier or his supporters. Senior Defence figures are privately furious about the intimidation of witnesses and efforts to portray the inquiry as a politically correct witch-hunt. They say the most serious allegations – which include the suspected brutalising or murder of prisoners – have been raised by SAS veterans who served in Afghanistan. Defence sources said it was unlikely the source of the threatening letters will ever be uncovered. They added that the senders appeared to want to scare witnesses from assisting the inquiry. The same sources said the letter has had the reverse effect, with more SAS soldiers agreeing to assist the Brereton inquiry, the most serious misconduct probe in recent Australian military history. Two hundred witnesses have so far been interviewed by Justice Brereton.

More than two dozen special forces insiders have told Fairfax Media that they back the work of the Brereton inquiry. Air Chief Marshal Mark Binskin. Credit:Jamila Toderas After Fairfax Media revealed the existence of the first threatening letter in June, then Defence chief Air Chief Marshal Mark Binskin described it as an abhorrent and illegal act. "I think it's absolutely disgusting that a disaffected person thought they could threaten a witness and look to influence the [war crimes] inquiry," Air Chief Marshal Binskin said. The fact that a second threat was sent shortly after the first had remained a tightly held secret in Defence. The first letter to the SAS soldier was sent within days of it becoming known inside the regiment that he may have testified before the Brereton inquiry.

It is understood soldier’s status as a confidential witness may have been revealed inside the regiment by a fellow soldier who spotted him at the inquiry, or, inadvertently, by a more senior officer who had knowledge of his inquiry attendance. Mystery also surrounds the role of Queensland paparazzo Nathan Richter, who helped send false information via email to authorities and The Australian newspaper about another serving SAS soldier. Defence sources said it was well known within the tightly knit special forces community that the soldier targeted by the Richter-linked emails was the author of a complaint about the awarding of a commendation to Mr Roberts-Smith, which had been forwarded to the Brereton inquiry. Loading The false information in the emails implied the SAS soldier may be poised to commit a violent offence, harming members of the public. It is unclear if the false claim was spread to intimidate the SAS soldier and there is no suggestion that Mr Roberts-Smith or any of his supporters were involved in sending it.

When contacted by Fairfax Media, Mr Richter refused to say who he was working for but confirmed he was working for a third party. “You send me a text and I can send it to someone who may be able to help,” Mr Richter said. An associate of Mr Richter said the photographer sent the information on behalf of a third party closely connected to a former SAS soldier. The federal police said in a statement it was “assessing” the threatening letters sent to the SAS in Perth and was liaising with the Defence Force investigation service over the emails that warned the SAS soldier may harm the public.