Police will tomorrow examine the original fingerprints taken from Robin Bain's body and test the firearm that was used to kill him and most of his family in 1994.
His son David served 13-1/2 years in prison for the murder of his parents and three siblings before being acquitted in a 2009 retrial. His defence team claims that Robin Bain was the killer.
The say that marks on Robin Bain's thumb, not made public until June this year, are consistent with him having fired the gun and prove David Bain's innocence.
Police have rejected the theory, saying the marks were cuts, but they will nonetheless carry out the tests in Christchurch tomorrow.
"This is being done to establish if greater clarity can be reached to explain the marks on Robin Bain's thumb as raised in the media in June," said Acting Assistant Commissioner (Investigations) Glenn Dunbier.