The case of Canberra's mystery prisoner was kept secret with the consent of everyone involved, the Morrison government says.
Senator Marise Payne has refused to release any details about the man known only as Alan Johns, during question time on Thursday.
The former military intelligence officer was tried, convicted and served out his sentence in secrecy, with even correctional officers at the Alexander Maconochie Centre left in the dark about why he was there.
But Senator Payne, representing Attorney-General Christian Porter, rejected a question placed on notice by Senator McKim to reveal what the charges against Johns were.
Greens Senator Nick McKim also asked how many other people had been charged, tried or imprisoned secretly in Australia in the past 10 years.
But Senator Payne said there were court orders that prevented any information being shared about the case.
"Those orders were made with the consent of the parties," Senator Payne said
"It is always at the discretion of the court including where parties consent, as to whether make such orders.
"In considering whether to do so the court balances competing public interests, including the principle of open justice."
This is a shocking example of secrecy and abuse of state power and our descent into a police state and yet another argument for a charter of rights in Australia.Greens Senator Nick McKim
But Senator McKim said it proved Australia needed a charter of rights.
"What we know now is in the 21st century there is a person secretly charged, secretly sentenced and secretly imprisoned in Australia," Senator McKim said.
"This is a shocking example of secrecy and abuse of state power and our descent into a police state and yet another argument for a charter of rights in Australia."
The legal fraternity and the ACT's Justice Minister Shane Rattenbury have also demanded an explanation about the case.
"I am deeply disturbed by the extraordinary levels of secrecy surrounding the 'Witness J' case: secrecy that is a direct result of the Commonwealth government's apparent growing disregard for the principles of open justice and a robust democracy," Mr Rattenbury said.
Retired ACT Supreme Court judge Richard Refshauge said the secrecy was "bewildering".
The case only came to light when Mr Johns took action against the prison in the ACT Supreme Court arguing an abuse of power.
His cell and brother's house were after prison management told police about a memoir he'd written behind bars as part of his mental health recovery plan.