A former intelligence officer who became a secret prisoner after a secret trial has surrendered a medal he earned in the Middle East while fighting Islamic State, saying he has been badly let down by his old employer.

Key points: Witness J received the Operational Service Medal for serving alongside elite special forces in Iraq

Witness J received the Operational Service Medal for serving alongside elite special forces in Iraq He was involved in Operation OKRA, Australia's contribution to the fight against Islamic State

He was involved in Operation OKRA, Australia's contribution to the fight against Islamic State He has accused his former employer of failing to upholds its duty of care

Witness J, a decorated Duntroon graduate who served 15 years across Australia's sprawling military and intelligence network, had wanted to return the medal in person to the director-general of the agency that employed him.

Denied that opportunity, Witness J instead handed his Operational Service Medal to the ABC, saying it was tainted by his former employer's lack of responsiveness to his mental health crisis.

To protect his identity, Witness J filed off the sides of the medal to remove his name before giving it to the ABC.

"I was proud to be awarded [the medal] but now it signifies to me the failure to discharge a duty of care to me and my other colleagues," Witness J told the ABC.

He was awarded the medal for serving alongside elite special forces soldiers in Iraq during Operation OKRA, Australia's contribution to the Middle East campaign combating Daesh, or Islamic State.

The circumstances of Witness J's treatment by his former employer and the legal system are now the subject of two high-powered independent investigations.

The chief of one of those investigations, James Renwick, has already declared that the unprecedented circumstances of Witness J's case were so extraordinary he "would not like to see [it] happen again".

"There has been an apparently unique set of circumstances whereby a person was charged, arraigned, pleaded guilty, sentenced, and has served his sentence with minimal public knowledge of the details of the crime," Dr Renwick said in his capacity as the Independent National Security Legislation Monitor.

The ABC, which revealed much of Witness J's story in December, has uncovered extraordinary new information about his case.

Witness J, a man in his mid-30s, served in East Timor, Iraq and Afghanistan.

Witness J has surrendered his Operational Service Medal in a rebuke to his former employer. ( ABC News: David Sciasci )

But it is when he served in a civilian role in a South-East Asian capital that his troubles began; troubles that culminated in him spending 15 months in prison.

Concerns had been aired back in Canberra about the way he was conducting himself as a single man on an overseas posting.

It was not an ideal time for such a claim to be voiced. Witness J was due to have his security clearance re-evaluated, a process that happens every five or so years in his type of work.

Witness J had been the victim of a drink-spiking incident during in-country language training at the start of his posting, which he had reported.

Witness J at CIA headquarters at Langley in Virginia. ( Supplied )

He had also taken a trip to Singapore during an Easter long weekend with a woman he had met on a language training course, without written approval and with a phone he should not, under departmental policy, have taken out of the country without first notifying Canberra.

Witness J claims he received verbal approval from a senior member at the embassy for his Easter long weekend travel, but that when he later sent a memo back to Canberra to report his trip he omitted mention of the approval, at the insistence of a higher-ranking diplomat.

Witness J's use of smartphone apps to contact diplomatic contacts was also against existing departmental policy, but again he claims this edict was routinely ignored by the many Australians posted to this country.

In late 2017, Witness J was notified that he would be recalled to Canberra as a result of his failure to report the full details of his unauthorised travel over the Easter long weekend.

Shocked that his top security "Positive Vetted" clearance was to be reviewed because of his behaviour, Witness J did what he now lives to regret.

He sent emails of complaint, over an unsecured network, back to Canberra, to the agency's head of security and a departmental psychologist.

In his communications, he named colleagues whose behaviour, he claimed, was more egregious than his own.

One senior colleague, he asserted, was known for his sexual escapades, including paying for prostitutes and strippers.

Witness J claimed the way he had been treated was outrageously hypocritical, insofar as he was being held to a standard higher than his superiors.

Witness J received the Operational Service Medal after serving alongside elite special forces battling Islamic State. ( ABC News: David Sciasci )

Witness J told the ABC that this episode had coincided with a mental health crisis, perhaps triggered by the death of close family members, as much as his service in various combat zones.

But his unwise and unprofessional emails of bitter complaint instantly transformed what might otherwise have been treated as a matter for internal departmental disciplinary process into a matter of criminal offence.

It is claimed Witness J, through his emails — and other communications back to Australia — not only broke strict rules of cyber engagement, but did something worse.

His employer claims Witness J's communications risked identification of foreigners who had been recruited by Australian officers for espionage.

Witness J's communications, over unsecure means, were a concern for intelligence agencies who feared their rivals' cyber capability.

After a secret trial in the ACT Supreme Court, he was sentenced in secret by Justice John Burns to two years and seven months in jail on February 19 last year.

He was released on August 16, after spending 15 months in Canberra's Alexander Maconochie Centre under a pseudonym.

The entire court proceedings were kept closed by an order made under the National Security Information (Criminal and Civil Proceedings) Act, which prohibited disclosure of the nature of Witness J's offending and the provisions under which he had been charged or convicted.

Little is known about Witness J's appearances in court. ( ABC News: Emma Machan )

Attorney-General Christian Porter has said the manner in which the case was wholly suppressed was unprecedented — a circumstance that challenges the principle of open justice, according to Dr Renwick.

"I intend to see whether I can make sensible, practical recommendations that, in a future case, where there might be an intention to have everything in secret, there can be at least some public notice and therefore some media involvement," he told a parliamentary committee last week.

The Inspector-General of Intelligence and Security, Margaret Stone, is expected to report on Witness J's case in the coming weeks.

Witness J said his extraordinary tale might never have been one to tell, had his former agency not failed him at a time of need.

"Three times I asked for mental health assistance and I was denied it. I was working overseas, I needed help and it … it never came," he told the ABC.

"I'm absolutely convinced that if I'd received help, none of this would have eventuated."

As for the medal he has surrendered, Witness J said: "On Anzac Day, I will be proudly wearing the medals I earned during my military service, but I will never wear that one again."