Sergeant Gary Silk and Senior Constable Rodney Miller were fatally shot in the Melbourne suburb of Moorabbin in 1998, while patrolling potential restaurant robbery targets.

At a 2002 trial, it was argued there were two killers - Bandali Debs and his criminal sidekick, 22-year-old Jason Robert. Both were convicted and jailed for life.

Roberts has always maintained his innocence, and on Tuesday became the first person in Victoria to have a second appeal heard on the grounds of fresh evidence.

Police are accused of deliberately manipulating evidence about the number of offenders at the scene, including in a statement from Senior Constable Glenn Pullin, who noted Sen Const Miller's dying declarations.

He claimed the officer, knowing he was mortally wounded, said that "they were on foot".

But it was revealed last year Sen Const Pullin's statement from the trial had actually been made 10 months after the murders and was passed off as the original, made four hours after the killings.

It's said that other officers lied about their recollections, that one officer had a practice of suggesting changes to statement and destroying originals.

Roberts' barrister, Peter Matthews, says the original was deliberately kept from the defence, the court and from prosecutors by police, and accused the Crown of minimising it as a case of non-disclosure of evidence.

"It's a lot more than non-disclosure. It's deliberate and extended an systemic concealment of the manipulation of evidence," he told Victoria's Court of Appeal.

"The rest of the trial may have proceeded in a different way in light of this body of fresh evidence."

Mr Matthews accused officers of breaching their sworn duty to the point of committing perjury.

It was such an extraordinary case that the judges must acquit Roberts rather than order a retrial, he said.

But Crown lawyer Ben Ihle argued the dying declaration evidence was just part of a larger body of evidence against Roberts, and had any potentially tainted evidence been excluded the jury would have convicted him anyway.

He pointed to transmissions to police communications at the time, alerting them "there's two offenders" and to "chilling" listening device evidence.

On the recordings Roberts described seeing police rushing to the scene - "they flew past us" - and talked of "having so much fun".

Mr Ihle said the fresh evidence in the case was not a central plank of the prosecution argument, and was the impugned evidence removed it "does not reduce the overall evidence".

But Justice Robert Osborn, one of three judges hearing the appeal, said if they were to order a re-trial Roberts' defence would want to include all the evidence, rather than have it excluded.

"They don't want to chop out one word or one sentence. They want it all in to show what you're left with is a very unsatisfactory picture," he said.

Mr Matthews said had the defence known about the multiple statements and other evidence, the entire defence case might have been run differently.

Roberts was in court for the appeal hearing.

He now admits he was involved in the robberies, but says he was with his girlfriend Nicole - Debs' daughter - when the murders happened.

The judges reserved their decision.

Australian Associated Press