We are not talking about one policeman giving questionable evidence but a series of officers lining up to lie to the Supreme Court at the behest of a team of investigators assigned to investigate the murders.

Make no mistake, the Roberts camp is claiming a Watergate-type conspiracy has left an innocent man in jail for decades.

The fallout has already been profound. The policeman who has investigated the case and believes Roberts' claims have merit, the respected former homicide senior sergeant Ron Iddles, has lost many friends in the job he loves. He knows it but is sticking to his guns.

Iddles, the former Police Association secretary, was recently the subject of a thinly veiled attack by the association president John Laird. "I'm outraged that a convicted police killer is afforded such a unique level of advocacy even after he has exhausted all legal avenues open to him," he wrote.

And how Iddles came to be the investigating officer will be discussed later.

But first the facts:

On August 16, 1998, Sergeant Gary Silk and Senior Constable Rod Miller were shot after they pulled over a suspicious car near the Silky Emperor Restaurant in Cochranes Road while on armed robbery stakeout duty. Silk died instantly but Miller was found about 170 metres away suffering from what would be fatal injuries.

Several police responded. One was Senior Constable Glenn Pullin. Much later evidence was given at the Supreme Court that Miller said to Pullin, "Silky's dead. Silky's dead . . . Help me, help me. Don't let me die."

Asked how many offenders there were the court was told Miller said, "Two. One on foot ... dark Hyundai ... I'm f---ed, I'm f---ed ... I'm having trouble breathing."

Miller's dying deposition that there were two offenders was vital as witnesses had only seen the driver in the car pulled over in Cochranes Road. The prosecution would allege the second offender (Roberts) was crouching down in the passenger well and couldn't be seen.

The two-offender theory was always the favoured version as the armed robbers targeted in the operation worked as a pair and the police were shot with two guns.

What is accepted is that the gunmen who pulled the series of armed robberies were Bandali Debs and his daughter's boyfriend, Jason Roberts.

Both were convicted of the police killings but Roberts now says he was with his girlfriend at the time and is not a murderer.

With all his appeal options exhausted his lawyers approached senior police saying Roberts could implicate Debs in a series of unsolved murders if they helped him get a re-trial. His request was rejected.

Later he made a second approach claiming Debs had implicated himself in the murders of Sarah MacDiarmid (at the Kananook railway station in 1990) and the murders of four women whose bodies were found at Tynong North.

It was during that police investigation that Roberts argued the prosecution had convicted an innocent man. It was then Ron Iddles examined the case and concluded that "On the basis of probability, he [Roberts] was not there."

How Iddles was put in charge of the case is not clear. Some police critics claim he took the case on without authority while Iddles says he was assigned the investigation.

What is certain is that it was contrary to established management practice as one of Iddles direct superiors at the time was Detective Superintendent Paul Sheridan, who was the head of the Lorimer taskforce investigations into the Silk-Miller murders, which means he was investigating his boss.

The latest development is a revelation in the Herald Sun that the original statement by Pullin taken hours after the shootings and witnessed by experienced homicide investigator Charlie Bezzina, was altered nearly two years later to include Miller's dying "they were on foot," words.

And so Pullin's version of events is vital but he remains psychologically damaged by the events of Cochranes Road.

He shouldn't have been on the road that night because he was still restricted by a reconstructed ankle that would never really recover but due to a staff shortage he sat in the passenger seat of the divisional van in Warrigal Road, near Chadstone, when the call came through of the police ambush.

Silk was already dead but Miller was clinging to life as the van turned into the street.

He had crawled nearly 170 metres away from the unmarked police car when he was found by Pullin and other officers.

"He knew he was dying. He was terrified and in agony. There was this big, fit policeman pleading for life and there was nothing we could do," he told me a couple of years ago.

In deep shock, Pullin wandered off by himself along Warrigal Road. "The next few hours are blank. I just remember sitting in the gutter and looking down to see a pile of cigarette butts at my feet, so I must have been there just smoking. All I can remember is seeing two blokes with shotguns run past. I don't know who they were."

He walked back to Cochranes Road and was eventually taken to a police station to make a statement for homicide detectives. "Looking back, I went to work that night and a different person came home."

Diagnosed with Post Traumatic Stress Disorder in 2001 he went on sick leave and two years later left the police force. He says he has no recollection of the second Silk-Miller statement and gave truthful evidence at the Supreme Court.

Iddles told 3AW's Neil Mitchell there should be a judicial inquiry into the case and that Pullin's altered statement would be key evidence. "Without Glenn Pullin saying I heard a conversation it all falls over. He's the person comforting him [Rod Miller] at the time."

Charlie Bezzina (with a well-earned reputation for honesty) can't recall signing the second version but raised the possibility an investigator asked him to re-sign and he did so without reading the document.

This would have been an enormous risk - for if Bezzina had read the document the conspiracy would have been uncovered.

But there were other police at the scene who say they heard Miller's dying words. Iddles says some also changed their statements years later. "Beware of the witness whose memory improves with the passage of time."

"This is not a Lone Ranger police officer going to another police officer [to commit perjury] ... there has to more than one person who knows about this."

If Roberts is the victim of a conspiracy he deserves justice. But as a convicted police killer he will struggle for public sympathy.

He will also struggle for political traction and while Attorney-General Martin Pakula says he would review any further petitions of mercy based on new evidence, the opposition will hardly take on his case in the run up to a law-and-order election.

There is one thing Roberts has not addressed. As a suspected police killer his arrest in July 2000 was carefully planned by the Special Operations Group.

In a fake plumber's van they pulled up at a building site to ask for directions from the apprentice carpenter and before he could speak armed police jumped from the back and dragged him into the van. In police circles it is called "The Snatch."

Frightened, bruised, intimidated and without legal advice Roberts was much more forthcoming with the men in black in the back of the van than he would be with detectives in an interview room.

"He said he did it," one said.