Independent National Security Legislation Monitor Grant Donaldson said information pertaining to why a former Commonwealth official with a high level security clearance had been imprisoned after a secret case should not have been withheld from public scrutiny in a hearing on Wednesday morning.

Additional information on the summary of the case was published on Tuesday after being reviewed by the government and consistent with the court's orders.

The new details provide a nearly 500-word summary of the former government employee, referred to as "Alan Johns" or Witness J, outlining the conduct that led to his arrest and imprisonment.

Mr Donaldson told the hearing there was no reason this information couldn't have been published at the time when he was prosecuted by an ACT court three years earlier.

"In this matter, the orders that were made were ultimately able to be published and there's no particular reason why, in my opinion, they could not have been published much earlier than they were," he said.

It marks only one of few public explanations for the case after former attorney-general Christian Porter first revealed the government's knowledge of it in a Senate question on notice in December 2019.

Witness J was secretly imprisoned in a Canberra jail for 15 months after being charged with disclosing confidential information in 2018.

The former intelligence officer was publicly revealed following a raid by Australian Federal Police of his Alexander Maconochie Centre cell in order to intercept a memoir he was writing of his situation.

The case sparked outrage among politicians and the public, including then-ACT justice minister Shane Rattenbury who had been unaware of the prisoner despite being in charge of the territory's corrections system at the time.

He was released from jail in mid-2019, 16 months before the end of his sentence.

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Mr Donaldson announced he would be reviewing whether section 22 of the National Security Intelligence Act was proportionate to national security threats in relation to its operation in the Witness J case.

The former Western Australian solicitor-general told a Senate estimates hearing in March he was considering launching further inquiries into the use of national security laws in the cases of Bernard Collaery and Witness K.

"I will be considering that matter at the appropriate time," Mr Donaldson said in March.

"There has been a great deal of disquiet concerning the invocation of the NSI Act in the circumstances of the Collaery matter."

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