Independent National Security Legislation Monitor James Renwick voiced concern about the trial.

"As far as we know there has never been another case, at least in peacetime in Australia, where all of it has been conducted in secret. That is something significant and different, and for my part I would not like to see it repeated," he told a Senate estimates hearing at the beginning of March.

"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."

Witness J was jailed for 15 months in Canberra's prison after a trial conducted entirely in secret - not only have the charges and findings been kept secret, but the orders covering non-disclosure have themselves been kept secret.

What has emerged is that Witness J was an intelligence officer, a Duntroon graduate who spent 15 years working for Australian agencies overseas including in Iraq and Afghanistan before running into trouble over an unauthorised weekend away while stationed in overseas. The fallout from that weekend led to him being charged.

He was jailed under the pseudonym Alan Johns, with ACT prison authorities kept in the dark about his identity and crime, and even ACT Justice Minister Shane Rattenbury not told.

Dr Renwick said "Mr Johns" had "communicated confidential information contrary to a lawful obligation not to do so. The information was of a kind that could endanger the lives or safety of others. This risk remains."

Under the court orders, "Mr Johns may disclose the fact of his conviction and terms of his sentence and that the nature of his offending involved 'mishandling classified information'. He may not otherwise disclose sensitive information including information that reveals the nature of his offending or the provisions against which he was charged or convicted," Mr Renwick said.

Announcing an inquiry and inviting submissions, he told the Senate there was "significant concern" about the case in legal circles.

He was to look at whether the media or a special advocate should be heard in cases where secrecy was to be invoked, whether at least some details of the charges and orders should always be made public, and whether the judge should be required to give reasons "for the exceptional step of departing from the strong presumption of open criminal justice".

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But this week, he said the inquiry had been dropped.

"The current COVID-19 pandemic has impacted [Dr Renwick's] ability to effectively engage with key stakeholders and the public, therefore preventing a thorough review to be undertaken at this time," his office said.

With Dr Renwick finishing his term on June 30, it was up to the new security monitor whether to hold an inquiry.