Blood on Robin Bain's shoes and tracksuit pants supports the theory that he killed himself, a jury in the High Court in Christchurch has been told.
The Crown accuses David Bain, 37, of killing his parents Robin and Margaret and siblings Arawa, Laniet and Stephen at the family's house in Dunedin on 20 June 1994.
The defence says Robin Bain killed the family present in the house before shooting himself.
The Crown says David Bain shot his family and tried to frame Robin Bain, but the defence says the forensic evidence suggests otherwise.
On Thursday, the court heard evidence from John Manlove, who runs a forensic laboratory in England and was asked to review the Bain case by the defence and conduct tests in 2008.
Though various Crown witnesses have ruled out the possibility that Robin Bain could have shot himself, Dr Manlove's analysis of photographic evidence supports the defence's theory that suicide was possible.
Dr Manlove says the direction of blood spots that fell onto Robin Bain's clothing fit with one of the poses the defence has demonstrated.
Crown scientists have testified that no blood was seen on Robin Bain's shoes. But Dr Manlove said he found spots of blood and tested them to establish that they came from Robin Bain.
He told the court it was more likely that Robin Bain was upright when the blood travelled to the shoe, which contradicts the Crown's suggestion that David Bain shot his father as he knelt to pray.
The court was told blood found on David Bain's socks probably got there by the accused walking on top of other blood, rather than it being airborne.
The Crown says blood found on David Bain's socks, which belonged to Stephen and Laniet Bain, flew onto his socks when he shot his family.
But Dr Manlove explained a different conclusion to the court, which supports the defence theory that David Bain only saw his siblings after they died.
He told defence lawyer Helen Cull, QC, that the blood spots on David Bain's socks were a contact stain, which was consistent with having walked over wet blood spots on the ground.
Laniet Bain evidence challenged
Dr Manlove on Thursday challenged the Crown's theory about the order of shots David Bain allegedly fired at Laniet Bain.
Pathologists who gave evidence for the Crown said that the first shot fired at Laniet Bain went through her cheek and she was still breathing and moving until two more shots were fired into her head.
But Dr Manlove says the shot in Laniet Bain's cheek was not the first one fired. He said the blood stain pattern showed she had not moved at all after the shot to her cheek.
Bloody fingerprints on gun disputed
British fingerprint expert Carl Lloyd told the court on Thursday David Bain's fingerprints on the rifle used to to kill his family members were not put there in blood.
Mr Lloyd's evidence contradicts that of a police fingerprint technician, who says David Bain's bloodied fingerprints were on the gun.
But Mr Lloyd told the court that, in his opinion, there was nothing to suggest that the prints were made with bloodied fingers.