Sergeant Gary Silk and Senior Constable Rodney Miller were shot dead on August 16, 1998 in Melbourne's sourth-east.

The police officers were staking out a Chinese restaurant after a series of armed robberies in the area, when they pulled over a car in Cochranes Road, Moorabbin .

They were gunned down shortly after the car was stopped.

Bandali Debs and Jason Roberts, who had committed several armed robberies together, were convicted of the murders.

But, almost 20 years after the officers were killed, the conviction of Roberts remains subject to conjecture.

Jason Roberts' conviction

Roberts, who was 17 at the time of the murders, claims he was not there when the officers were shot.

But in 2002 he was convicted and sentenced to life with a minimum 35 years in prison.

The conviction was reviewed by decorated homicide detective Ron Iddles in 2013.

Mr Iddles' review called into question whether Roberts was there on the night of the shooting, and Mr Iddles believed that on the basis of probabilities he had not been involved.

The evidence that placed Roberts at the scene was a statement by Senior Constable Glenn Pullin, who gave evidence that Senior Constable Miller told him in his final breaths: "they were on foot".

It was argued that this proved more than one person committed the murders.

But News Corp reported on Tuesday that the statement was falsified; an original version made no mention of Senior Constable Miller describing more than one shooter.

There was other evidence that appeared to indicate there was only one person at the scene on the night of the murders, including statements from other police, and eyewitness accounts.

In July this year, Roberts' then-girlfriend - Debs' daughter - indicated she would be willing to testify that she was with him on the night of the murders.

The reaction to the 'false' statement

The "false" statement was signed by another decorated former homicide detective, Charlie Bezzina.

"When I learnt of these two statements two weeks ago, I was floored," Mr Bezzina told radio station 3AW on Tuesday.

Mr Bezzina said it was the first time he had seen the statement which mentioned a conversation about multiple offenders.

"That one is the statement that I took, without the conversation, and this second one dated the same time and date with my signature, I've never seen it before."

Mr Iddles said the statement provided evidence of corruption and a conspiracy.

"This is not a lone ranger police officer going to another police officer and saying 'listen, by the way, I want you to add some conversation in here, I want you to come to the Supreme Court and I want you to perjure yourself'," he told 3AW.

"There has to be more than one person who knows about this, if you have more than person, you have a conspiracy."

He called for a judicial review into the case.

Leading Melbourne lawyer Rob Stary, who is representing Roberts, said the statement went to a critical issue, and he believed the existence of two statements was not known to Roberts' lawyers at the time of the trial.

"It goes to a very critical issue and the issue is whether there was one or two shooters that were identified, or two persons being present at the scene," he said.

"This is a fundamental issue because, in fact, if the only person that's identified at the scene is ultimately Bandali Debs, he's the psychopathic shooter, and it doesn't make reference to a second person, it's very fundamental."

What now

Roberts had a petition for mercy denied by Attorney-General Martin Pakula in March.

It is his final chance at freedom, as the Andrews government introduced laws last December that prevent anyone convicted of murdering a police officer from being released on parole.

The Independent Broad-based Anti-Corruption Commission is investigating the reported discrepancies in Mr Pullin's statement after the matter was referred to them by Mr Iddles on Monday.

Mr Iddles is himself being investigated by the police Professional Standards Command for his conduct during the investigation.

Chief Commissioner Graham Ashton has described the complaint about Mr Iddles as related to the "manner in which the investigation was conducted" and a serious issue, but little other detail is known about what is alleged.

What's at stake now?

Either not much or a lot, depending on how the cards fall.

IBAC could find evidence that the statement is false, and charge those responsible. That could, in turn, increase pressure on the Attorney-General - whoever that may be when the investigation is finished, given the state election is little more than a year away - to grant the petition for mercy.

Or the watchdog could find evidence that the statement is false, but not enough to support charges. That would create less of a compelling case for appeal.

Either way, Roberts has only one way out - through the door of the Attorney-General. If the petition for mercy is granted, the case is either referred to the Court of Appeal, or a question about the petition is referred by the Attorney General to the Supreme Court for an opinion.

Neither of these options guarantees his release.

In essence, the entire case against Roberts could be proven to be false and it still may not be enough to free him.

The implications for the force and former officers such as Mr Iddles and Mr Bezzina (and others yet to be named who will undoubtedly be drawn into the mire) are less clear. But it is, for the most part, only their reputations at stake - not a lifetime in prison.