A man jailed for life for the killing of two Melbourne policemen has had his convictions overturned because of the "reprehensible" conduct of investigating officers.
Jason Roberts had convictions for the 1998 murders of Sergeant Gary Silk and Senior Constable Rodney Miller overturned on Tuesday, after two decades behind bars.
His lawyers have flagged plans for a bail application after three of the state's most senior judges ordered he remain behind bars before a retrial.
Roberts and Bandali Debs were found guilty by a jury in 2002 and sentenced to life in prison. Roberts has served 20 years of the now overturned minimum 35-year sentence.
The Silk and Miller families say they're devastated by the court's decision and continue to support the Taskforce Lorimer investigators.
"It is not the decision we were hoping to hear, 22 long years after Gary and Rod were murdered," they wrote in a statement.
"We are deeply saddened for the members of Taskforce Lorimer, who have dedicated so much of their lives to ensuring that Rod and Gary received justice."
The appeal judges said after anxious consideration they determined the long-undisclosed misconduct of one particular officer had so corrupted Roberts' initial trial "as to poison it to its root".
Senior Constable Glenn Pullin destroyed his original statement about the murders and four months later substituted a backdated statement which included dying declarations of Sen Const Miller, indicating there were two offenders.
"They were on foot," he claimed the officer, knowing he was mortally wounded, had said.
Sen Const Pullin then committed perjury by lying about the second statement, and failed to disclose its existence, which the court found amounted to a "gross and fundamental corruption of the trial process".
Initial statements of four other officers were not included in a brief of evidence and are now missing, and it was revealed a senior detective initially told officers not to include Sen Const Miller's dying declarations in their statements.
The judges concluded it would not be unfair or unjust for Roberts to face a fresh trial.
While they are not convinced conviction is inevitable, they noted the Crown's case remains strong.
"Although the non-disclosure did not result from innocent mistake and reflects reprehensible conduct by police officers, we do not accept that the need to deter repetitions of such behaviour is of itself sufficient to justify an acquittal," they said.
"The quashing of the appellant's convictions and the fact of a retrial will themselves have a deterrent effect."
Roberts has been in custody since August 2000, when he was 19 years old.
He has always maintained his innocence in the murders. While he admitted being involved in robberies with Debs, he says he was with his girlfriend Nicole - Debs' daughter - when the officers were killed.
Anti-corruption watchdog IBAC has also investigated the allegations of police wrongdoing and handed down a report in July slamming Victoria Police for improper evidentiary and disclosure practices, some of which had been taught at the Victoria Police Academy.
Because Victoria Police had never clearly called out or stopped improper practices there was a risk they continue to be used, Commissioner Robert Redlich found.
Victoria Police has been contacted for comment.