The information only came to light in 2008, when the jury foreman contacted Montaperto's counsel to say he had received information during the appellant's trial linking him to the Cormack case.
The juror said he was made aware of the connection by a work colleague who had two brothers who were police officers.
The juror maintained however, that the jury's decision has been reached on evidence alone.
An inquiry of the jurors was directed by the Court however, only six of the 12 could be contacted, some having died in the three decades since the original trial.
Of those spoken to, two did not believe Montaperto's link to the Cormack cases had come up during trial and another two recalled being made aware of that fact possibly during the trial.
Justices Peter Kos, Forrest Miller and Patricia Courtney said it was sufficient to amount to a miscarriage of justice if just one juror was "infected".
"But here there was a credible basis to say that other jurors had received the information, and an adverse impact on their weighing of the evidence could not be excluded," their decision read.
Although the information was passed on to other jurors "ignorantly and naively, rather than maliciously", the Justices found the information was highly prejudicial having come from police officers.
"It was more than rumoured connection."
The Justices found that a "clear case of apprehended jury bias" had been established and that the verdicts were therefore "unsafe".
"We have found this case involves the transmission of materially prejudicial extraneous information to the whole jury.
"We are satisfied that this transmission created a real risk of miscarriage of justice.
"The appellant did not receive a fair trial.
"The verdicts entered in 1988 were unsafe and must be set aside."
No new trial was ordered given the amount of time and that Montaperto had long since served the sentence imposed.
The convictions were quashed on April 22, this year.
