Former detective Ron Iddles believes Jason Roberts wasn't present at the 1998 police murders.
For the families of slain Melbourne police officers Gary Silk and Rodney Miller, the distress has stretched almost two decades.
The pain has been reignited this week as headlines again raise doubt over the conviction of one of two men, Jason Roberts, jailed for their murders.
Roberts always maintained his innocence throughout a Supreme Court trial and unsuccessful bid to the Court of Appeal, and was finally refused any avenue of further appeal by the High Court.
He has served some 15 years of a life sentence for the deaths of the two officers who were fatally shot while on duty investigating a series of robberies in Moorabbin in 1998.
Decorated former homicide detective Ron Iddles, who reviewed the case against Roberts in 2013 at the request of the DPP, has subsequently cast further doubt over Roberts' conviction in news that has upset the victims' family.
"Over the past 19 years, the tragic events of August 16, 1998 have been constantly reignited at great distress to our families," the officers' families said in a joint statement on Tuesday.
"The police force has rejected the Iddles Report.
"There must come a time when we as a family can feel confident that the process is now over. There must come a time, when we say enough is enough."
Mr Iddles believes Roberts wasn't present at the murders of Sergeant Silk and Senior Constable Miller, and that fellow convicted murderer Bandali Debs was the lone gunman.
He has signed an affidavit to that affect, the Herald Sun reported, but the former detective would not comment when contacted by AAP.
"In respect of Jason Roberts, it's not appropriate that I make any further comment," he said.
Police Association secretary Wayne Gatt said the murders were "one of the most shocking crimes" against officers in living memory.
"People can have their views, but due process has been followed to its end point," Mr Gatt said.
Attorney-General Martin Pakula said he rejected Roberts' 2016 petition of mercy after receiving legal advice.
"There would need to be, in my view, extremely compelling evidence to reopen a case which has already been before the courts three times," Mr Pakula told 3AW on Tuesday.
"I took the view that that extremely compelling evidence didn't exist."
Roberts and Debs were convicted in 2002 based on evidence including telephone intercepts and listening devices which prosecutors inferred knowledge and details of the murders that would only be known by the offenders.
Mr Pakula said he requested "significant additional information" and advice while reviewing the case, but ultimately he rejected the petition.
"There was enormous amounts of audio tape evidence that was educed at trial. There were I think something like 137 prosecution witnesses. There were 87 days of trial," Mr Pakula said.
"It's important to remember that Jason Roberts never took the stand in his trial.
"He did not make himself available for cross examination at trials where claims ... could have been tested."