It could be weeks before results are known from today's re-examination of the original fingerprints taken from Robin Bain's body and testing of the rifle that was used to kill him and most of his family in 1994.
David Bain, Robin's son, served thirteen-and-a-half years in prison for the murder of his parents and three siblings before being acquitted in a 2009 retrial.
His defence team claims Robin was the killer.
They say marks on Robin Bain's thumb, not made public until June this year, are consistent with him having fired the gun, which proves David Bain's innocence.
Police have rejected the theory, saying the marks were cuts, but they are nonetheless carrying out the tests in Christchurch today.
Advocates for David Bain, now aged 41, have been invited to the behind-closed-doors scrutiny by police fingerprint and firearms experts, along with ESR scientists, but the media have been told to stay away.
The time and location of the testing has not been revealed by police, and today long-time supporter Joe Karam thought it was right to tow the police line.
"Police are not wanting to reveal anything, and so I'm not going to say anything either,'' he said.
Acting Assistant Commissioner (Investigations) Glenn Dunbier says it will be some time before the outcome is known.
"We won't have any answers by the end of the day,'' he said.
"The test results will be subject to a proper scientific analysis by accredited experts and may take some weeks to complete.
"Until we have the full results of the analysis our position remains that any explanation for the marks remains a theory.
"As we've said before it also remains a real possibility that, even after the analysis is completed, there will still be no definitive conclusion regarding the marks.''
Last week, Mr Karam said he was "very confident'' that the original fingerprints will show that there are no cuts on Robin Bain's thumb and forefinger where the black marks were.
"The only proposition they've (the police) put forward so far is that they're cuts from rose bushes or something,'' he said.
"Well, I can tell you now with a great deal of confidence, the fingerprints will not reveal any cut.''
The marks apparently went unnoticed for 19 years until TV's 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.