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.
The marks on Robin Bain's thumbs came to light in June on TV3's 3rd Degree programme.
They had been unnoticed for 19 years until a gun expert 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.
But 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''.
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.''
David Bain's advocates would be present at these tests, Mr Dunbier said.
"The results will be subject to a full scientific analysis and it is likely to be several weeks before the outcome is known.''
Opposing views
Joe Karam says: The marks on Robin Bain's fingers cannot have been cuts because they were not present in the first set of fingerprints taken after he died. Police have misled the public by only releasing the second set of prints, which show the marks, deemed to be cuts.''
Police say: "The second set of prints are accurate. The first set of prints was taken by a detective, the second by a fingerprint expert who determined the first set were not adequate.''
