David Bain's fingerprints were found on the rifle used to kill five members of his family, a jury at the High Court in Christchurch has been told.
David Bain, 37, is accused of shooting his parents Robin and Margaret and siblings Arawa, Laniet and Stephen at the family home in Dunedin on 20 June, 1994.
The defence says Robin Bain killed the family present in the house before shooting himself.
David Bain owned the rifle that was used in the killings, and the defence says it is therefore no surprise that his fingerprints were found on it.
But evidence from Kim Jones, an internationally recognised police expert on fingerprints, at the retrial on Thursday showed that the prints on the rifle belonged to David Bain and his brother Stephen.
There were no prints on the rifle belonging to Robin Bain, whom the defence is the real killer.
Mr Jones told the court he examined the weapon the day after the killings and found two sets of prints.
He was later asked to compare those prints with some taken from David Bain and found one of the sets matched perfectly.
Mr Jones told the court the prints on the rifle were David Bain's and that he had "absolutely no doubt about that". He said he thought the prints were made in blood and were sharply defined.
Mr Jones demonstrated how a powerful, forceful slapping motion down into the rifle would have created them and said they would not have been made by someone who had simply picked the rifle up.
He told the court he was also able to identify a partial palm print found on the side of the family washing machine in which the Crown says David Bain put his bloodied clothing after killing his family.
He said the partial print belonged to the accused.
Robin Bain 'peaceful and gentle'
Earlier, witnesses told the court Robin Bain was a peaceful and gentle man.
Robin Bain was the principal of a two-teacher school when he died in 1994.
The other other teacher at the school, Darlene Thomson, described him as a peaceful man and recounted a story about him saving a spider from students who wanted to kill it, telling the students everything had a right to live.
The former chair of the board of trustees at the school, Dorothy Duthie, said Robin Bain was kind and caring.
Ms Duthie said she was surprised at his reluctance to use a rifle during an incident at the Tairei Beach School when a possum was caught in a trap.
She said when she put a pellet in her air rifle and handed it to Robin Bain to use on the possum, he put his hands by his side and stepped back.
Ms Duthie told the court she found that unusual.