Last week, police successfully fought a freedom of information bid to release internal investigations into the sergeant who led the flawed investigation of rape and assault allegations.

The allegations against the ACT prison guard were made by his former girlfriend, then a NSW police worker, in 2013 and 2014.

She alleged he bashed and raped her, allegations that saw him locked up for four months in Goulburn, placing him in considerable danger due to his job.

The allegations, made in the midst of a bitter property dispute between the pair, were later found to be false.

Now, the prison guard is suing for wrongful imprisonment.

He also lodged a freedom of information application, seeking material about internal investigations of the sergeant who led the flawed investigation.

The Australian Federal Police, following a lengthy delay, rejected the vast majority of the FoI application, but the guard appealed.

He took the matter to the Administrative Appeals Tribunal, where the AFP again argued against the materials' release.

It was argued that releasing the documents publicly would compromise the integrity of the AFP's professional standards process, which relied on complaints being treated confidentially.

Last week, the tribunal found in police's favour, saying it was not in the public interest to release the documents.

The guard, who still cannot be identified for legal reasons, described the decision as a "bit rough".

He questioned why documents were being withheld despite the fact that the investigation of him, codenamed Operation Verdigris, was concluded years ago.

He suspected police were in "damage control", knowing that the release of the material would be embarrassing.

"I think it's going to expose how they handled themselves internally. I think it's going to show how incompetent they are as well," he said.

"With any business or government agency, the last thing you want is people to have no faith in you or to look bad in the public eye.

"I do believe they've gone into a bit of damage control, they know what they're up against. They obviously have some material, they know how exposed and vulnerable they are."

Following the guard's release, it was revealed he had strong alibi evidence proving that he could not have raped his ex-partner.

The woman was charged with making false accusations, and later convicted.

She is currently appealing.

The guard's family have complained to the AFP, the Justice and Community Safety Directorate, the Director of Public Prosecutions, Attorney-General Simon Corbell, and others.

They say they are yet to get any satisfactory response.

The guard's father said the attempts by police to keep documents secret showed how far they would go to protect reputations.

"The AFP go to great lengths to cover and protect their own from any public scrutiny or accountability," he said.

"Additionally after letters to the Attorney General, the ACT Law Society and the Justice and Community Safety Directorate it now appears that the DPP is answerable to no one and can ruin lives with absolutely no recourse."

"This whole thing stinks and needs to be brought to the public's knowledge."