Roberts was convicted in 2002 over the murders of Sergeant Gary Silk and Senior Constable Rodney Miller, but it was overturned by Victoria's Court of Appeal earlier this month.

He faces the prospect of at least another 12 months in jail before a new hearing.

Supreme Court Justice David Beach said he had no basis for concluding the prosecution case was anything but powerful.

But he noted, as did the appeal court, that conviction was not inevitable.

"That assessment, coupled with the fact that the alleged offending in this case is so serious, tells against a grant of bail in this case at this time," he said.

Roberts' lawyers claimed in an application earlier on Thursday that the case against him was not as strong or powerful as prosecutors claimed.

Peter Matthews said transcripts of secret listening devices made by police decades ago were significantly less incriminating when translated by experts.

The defence team has spent spent tens of thousands of dollars already having expert linguists redo police transcripts of the "indistinct" recordings used in Roberts' original 2002 trial.

"The content is significantly less inculpatory when transcribed by an expert, to the point of not inculpatory at all," Mr Matthews said.

In quashing the original jury verdict, the Court of Appeal found it was not inevitable that Roberts would be convicted again, but the case was strong.

Mr Matthews said that was not necessarily the case, when considering the evidence as it would be presented in a fresh trial.

Justice Beach said a trial could begin in late 2021, but Mr Matthews said 2022 was more likely.

The defence team has also spent a significant sum of money on expert scientific reports, including around the evidence about whether one or two shooters were involved.

Roberts has admitted - and will maintain in a fresh trial - that he was involved in a series of robberies with Bandali Debs, who was also convicted of murdering Sgt Silk and Sen Const Miller.

Roberts has always maintained his innocence in the murders. Debs is serving a life sentence and has not appealed.

Mr Matthews said another aspect of the new trial would be the fresh defence evidence about an alibi, from both Roberts and his then-girlfriend Nicole Debs - the daughter of Bandali Debs.

The barrister said the fact alone that he had spent 20 years behind bars after a trial "corrupted" by Victoria Police was exceptional enough in itself to justify bail.

Roberts has been in restrictive custody since 2013 and coronavirus restrictions since March this year had compounded the weight of imprisonment on him, Mr Matthews said.

Prosecutor Ben Ihle SC conceded the 20 years Roberts had already spent in custody was a point in favour of granting bail but said he was coming up against an undeniably strong or powerful prosecution case involving extremely serious allegations.

Justice Beach acknowledged that if Roberts was to be convicted and receive the same sentence, he would have only have served a fraction of it.

Australian Associated Press