Bain campaigner Joe Karam said the evidence in question was crucial in convicting Bain of the murder of his father, mother, two sisters and brother in Dunedin in June 1994.
Bain was convicted on five counts of murder on May 29, 1995, but in May 2007 the Privy Council found a substantial miscarriage of justice had occurred, quashing the convictions and ordering a new trial.
The defence team last week filed an application asking the Privy Council to acquit Bain based on new evidence unavailable at the original appeal.
Mr Karam said the defence team would ask the Privy Council to recall its decision, with the evidence set to show "someone else was the killer".
He declined to elaborate.
Bain was pleased about the approach as "in 15 years the best result has been at the Privy Council", Mr Karam said.
The application, which took several months to prepare, was sent to the Privy Council last Friday.
Mr Karam would travel to England next week on matters relating to the case.
Michael Reed QC said the defence team had been working on the Privy Council approach "for a while".
"As a result of new information, we think [the Privy Council] is justified to change their decision."
Mr Reed denied the move was a delaying tactic by the defence: "Absolutely not. No way . . . We don't want to delay it. We want to get rid of it."
Bain wanted the matter settled and "out of his life", Mr Reed said.
Even if the petition was not successful, the defence was still "on schedule" for the retrial, set to begin on February 16.
The Otago Daily Times understands legal aid has already been granted for the petition to the Privy Council.
Crown Law spokeswoman Jan Fulstow, of Wellington, and Detective Senior Sergeant Kallum Croudis, of Dunedin, declined to comment while the matter was before the courts.
University of Auckland law authority Associate Prof Scott Optican said the filing of an application to the Privy Council was an unusual move by the defence team, as it already had a retrial approved.
"They went to the Privy Council last year to present new evidence to get a new trial and they are now going back to say they have even newer evidence to say they don't want a trial."
The only reason to return to the Privy Council with the forensic evidence was if the defence team believed it would not get a fair trial, or there had been an abuse of legal process, he said.
"I don't know the likelihood of success. They would have to have something pretty substantial."
When the Privy Council granted the original appeal it reserved judgement on whether Bain was guilty or not guilty.
"That is what judges and juries are for."
