Police may be forced to properly investigate secret new claims of Mafia involvement in the assassination of Colin Stanley Winchester before prosecutors can push ahead with a retrial of David Eastman.
Mr Eastman, 68, has been out of prison since Friday night, when he was released after 19 years behind bars for the assistant federal police commissioner's murder in January 1989.
The ACT Supreme Court quashed his conviction and ordered a retrial after revelations earlier this year that gunshot residue analysis used to link him to the murder scene was deeply flawed.
The court also used Friday's decision to take aim at the Australian Federal Police for not seriously investigating new but untested claims casting suspicion on the Calabrian Mafia, or 'Ndrangheta.
The organised crime syndicate are said to have had a motive to kill Mr Winchester, believing he double-crossed them during an investigation into drug crops in NSW.
The Director of Public Prosecutions is in the process of deciding whether to push ahead with a second trial of Mr Eastman, decades after the crime.
But, in Friday's judgment, justices Steven Rares, Michael Wigney and acting justice Dennis Cowdroy warned that the DPP may need to tell the AFP to properly investigate the new Mafia evidence.
"The proper investigation by the AFP and assessment by the Director of that material and any such investigation will be germane to the exercise of the Director's discretion to proceed with a new trial," they wrote.
"It would appear to us, from the confidential material, that the investigation of this material to date may have been unsatisfactory and deficient."
The court said it would be reasonable to expect the DPP would "request or require" the AFP to conduct further investigations into the highly sensitive material.
"[Particularly] in light of some of the apparent deficiencies in both the original investigation into the alternative hypothesis and the investigation of the new material that has occurred thus far," it said.
The new evidence, which was heard in highly restricted confidential hearings before the inquiry earlier this year, is said to take suspicion of Mafia involvement beyond the mere speculation that has previously existed.
The claims are described as now potentially at a level of a "reasonable hypothesis consistent with Mr Eastman's innocence".
But they are still untested and internal documents show the AFP was reluctant to reinvestigate areas already looked into by Operation Peat, the team who originally investigated Mr Winchester's murder.
On Monday, ACT Policing declined to publicly comment on whether it would look at the new evidence, saying it would be inappropriate to make a statement given a retrial of Mr Eastman had been ordered.
The DPP had not previously seen the secret material.
But the order for a retrial is expected to require that prosecutors be given the new material, the court said on Friday.