Police say marks on the hand of Robin Bain do not prove that David Bain is innocent of killing five members of his family.
David Bain spent 13 years in prison but was found not guilty in a retrial in 2009 of killing his family, including father Robin Bain, at their Dunedin home in June 1994. He is seeking compensation.
His legal team has investigated new evidence that it says proves that Robin Bain committed the murders before killing himself.
Mr Bain's lawyer Michael Reed, QC, told Radio New Zealand's Morning Report programme on Thursday that distinctive marks in a photograph of Robin Bain's thumb show that he fired a gun on the morning of the deaths.
Mr Reed said while the evidence for David Bain's innocence is already strong, this is the final clincher and the Government should get on with awarding compensation.
But Assistant Police Commissioner Malcolm Burgess said on Thursday the markings are open to several interpretations by experts and could be minor abrasions or cuts.
Mr Burgess said fingerprint experts say prints taken from Robin Bain show gaps where the markings appear, which could suggest they are small cuts.
He reiterated that the only identifiable fingerprints on the rifle used in the killings belonged to David Bain.
Mr Burgess said police would continue to look into the issue to better understand what the photographs show.
Prime Minister John Key said he doesn't have a view on the material and Mr Bain's compensation claim has been deferred while part of the case goes before the court.
Mr Key said after the court process the Government would take advice and move to reconsider whether compensation will be given.