New tests will be carried out on the gun used in the Bain family murders next week.
The tests will by done by police with David Bain supporter Joe Karam and forensic scientists present.
Mr Karam announced today that police would be examining original fingerprints and conducting tests on the gun used in the murders in June 1994.
The development comes after claims in June that a photo of Robin Bain's body showed parallel markings on his thumb consistent with him having fired a gun on the morning of the killings - apparently proving his son's innocence.
Police rejected the theory, saying the marks were cuts.
"The Bain team, myself and forensic people will be in attendance and I'm very confident that the original fingerprints will show in fact that there are no cuts on (Robin) Bain's thumb and forefinger where the black marks were," Mr Karam said today.
"If the fingerprints don't show cuts police are going to be left in the position of saying 'what are these sooty black lines?'
"The only proposition they've put forward so far is that they're cuts from rose bushes or something. Well, I can tell you now with a great deal of confidence, the fingerprints will not reveal any cut."
Mr Karam would not reveal when or where the tests would be held.
David Bain had been invited to attend but he would be busy at work, Mr Karam said.
A police spokesman said tonight that the decision to re-examine Robin Bain's fingerprints was made in June in response to TV3's 3rd Degree programme.
"What we said in June was an examination of the original photograph does not give any definitive indication of what the marks could be.
"There are other possibilities, including that they are minor cuts - we know for example, he was doing work on the roof."
Police had never definitively said what they believed the marks were, the spokesman said.
"Anything at the moment is just a theory ... it might well be that we do all this testing and get no closer to a definitive explanation for them."
He would not speculate what could happen should the tests prove they were gun marks on Robin Bain's fingers.
Earlier today Acting Assistant Commissioner (Investigations) Glenn Dunbier said police hoped the examination would provide "greater clarity" on what caused the marks.
"It also remains a real possibility that even after the originals have been examined there will still be no definite conclusion regarding the marks," he said.
Police had announced last month they would be applying to the court for access to the originals of the fingerprints taken from Robin Bain, Mr Dunbier said.
"These will be examined thoroughly to see if they assist in determining the nature of the marks on Robin Bain's thumb.
"As part of this process police will also carry out tests on the firearm and the magazines involved."
"The results will be subject to a full scientific analysis and it is likely to be several weeks before the outcome is known," Mr Dunbier said.
The marks on Robin Bain's thumbs had apparently gone unnoticed for 19 years until 3rd Degree revealed that a gun expert had re-examined photos of Robin Bain's hands, and said the marks matched those made by gunpowder residue when loading the magazine of a rifle shortly after it had been fired.
At the time, Assistant Commissioner Malcolm Burgess said Robin Bain's fingerprints showed patches on the thumb, suggesting cuts from "handyman" work.
"Marks on a photograph can always be open to several interpretations by experts ... Examination of the original photograph does not give any definitive indication of what the marks could be," he said.
Last month, Mr Karam said a second set of photographs of Robin Bain's thumb further supported the theory. That set of fingerprints was taken on June 21, 1994, the day after Robin Bain died, and were "perfect" prints with uninterrupted ridge lines, he said.
The prints police had referred to were taken on June 22, 1994, after Robin Bain's body had been moved in and out of refrigeration in the mortuary.
Mr Karam said a fingerprint expert confirmed that the change in the body's temperature would have caused condensation on his hands.
When the second set of prints were taken, some ink would have been repelled by the presence of moisture, causing "blotchy white marks".
Justice Minister 'thoroughly politicised' case.
The retired Canadian judge appointed to independently review Mr Bain's bid for compensation says Justice Minister Judith Collins has "thoroughly politicised" the case.
Mr Bain's legal team today concluded their submissions applying to the High Court at Auckland for access to about 250 documents Ms Collins received over the compensation claim.
Yesterday, an email presented to the court showed Ms Collins' staff were seeking to stop Canada's Justice Ian Binnie from going "completely feral".
An email sent from Ms Collins' press secretary Rachael Bowie to Ms Collins, her senior private secretary and senior adviser, said Justice Binnie needed to be kept "in the tent for as long as possible" to avoid his "very damaging" report from being released.
When approached for comment, Justice Binnie said "Thanks for the opportunity, but as the Minister has thoroughly politicised the Bain issue I think I should refrain from any comment.
"What I have to say about the Bain case is in my report, submitted to the Minister almost a year ago."
At the High Court today, lawyers representing the Justice Minister told Justice Patrick Keane the documents were protected by lawyer-client privilege, but Mr Bain's team argued the privilege had been waived because the Minister's legal advisers acted improperly and unethically.
Yesterday, Mr Bain's lawyer Michael Reed QC, said Ms Collins should step aside and another minister be appointed due to her handling of the case, which he described as biased and prejudiced.
He said Ms Collins was acting as the Minister of Police, not the Minister of Justice, and was struggling to distinguish between the two.
The entire process had been hijacked by Crown Law and police, Mr Reed said.
This morning, he said the way the case was handled was "hopelessly compromised".
Ms Collins' lawyer Kristy McDonald QC, responded by wholly rejecting these claims.
"It is important I say there is not a shred of evidence to support such serious allegations."
This was not a substantive hearing and should not be an opportunity for "unprincipled rhetoric" to be brought before the court, she said.
Mr Bain's lawyers have argued that Crown Law had a conflict of interest in advising the Minister on the compensation claim, as she was their employer.
Mr Reed said even if there were staff in the Crown Law office involved in the proceeding who may be independent, the majority were "our adversarial opponents".
Because of this, he argued, they were not upholding the standards required of the legal profession and therefore were not protected by lawyer-client privilege.
Ms McDonald said just because they were "in-house" lawyers did not mean they lacked the ability to act independently and impartially.
"We're talking about 20 per cent of the legal profession ... who are employed in that capacity. It would be an extraordinary proposition to suggest that the advice that they provide does not attract privilege," she said.
"We do put on different hats all the time - it's part of the skill of being a legal advisor. It doesn't mean that you're necessarily conflicted. And Crown Law particularly do that."
The Bain legal team's allegations had been taken to an "extraordinary" level with suggestions of conspiracy and improper motive, which were "just nonsense", Ms McDonald said.
When approached for comment, Ms Collins declined, saying "it would be completely inappropriate for me to make any comment regarding this matter, at this stage".
Mr Bain was not present at the proceedings.
Justice Keane has reserved his decision.