Dr Kenneth Thomson, a consultant with 30 years' experience in pathology, 22 years of that with forensic autopsies, is one of three pathologists the Crown is calling in the retrial of David Cullen Bain for the murder of his parents, two sisters and younger brother in their Every St home 15 years ago.
Bain, now 37, denies killing them. The defence says Robin Bain killed his wife Margaret, daughters Arawa and Laniet and younger son Stephen while suffering from serious depression and that he then turned the gun on himself. Robin's motive, the defence contends was that Laniet was about to expose his incestuous relationship with her.
David Bain told the police he found the family all dead when he returned home from his early morning paper round.
But the Crown says David killed all five members of the family, that he shot his mother, and siblings - Stephen once, then fatally, after a violent struggle, Laniet three times, and Arawa once - and then waited for his father, shooting him from behind curtains in the front room.
He then left a message on the computer "Sorry, you are the only one who deserved to stay" to make it look like Robin Bain was responsible.
The hearing before Justice Graham Panckhurst and a jury of seven women and five men has now been running for 23 days. It is expected to take up to about 12 weeks. Evidence has been heard from about 70, almost half, of the Crown's witnesses.
Much of the forensic evidence has focused on the wound to Robin Bain's left temple area and the likelihood of a right-handed man choosing that particular site and being able to hold the silenced Winchester .22 at the angle necessary to create the wound trajectory when he shot himself.
Earlier this week, Dunedin pathologist Dr Alexander Dempster said he thought it most unlikely someone of Robin Bain's height and arm span could have used the rifle to commit suicide, but after seeing photographs from a defence expert of various scenarios, he agreed it might have been possible, although "not particularly easy", for Robin Bain to reach the trigger in one of those positions.
His height and arm span were about the same as Robin Bain's, Dr Dempster said, and in the tests he did he had not been able to find a position where he could reach the rifle trigger using his right hand. He could just reach it with the middle finger of his left hand.
But his demonstration to the court involved holding the rifle in the air and against his head while the defence depictions were of a man standing and leaning over the weapon, with the butt on the floor or resting on a chair.
He thought if Robin Bain had used the rifle on himself while standing in one of those positions, he would have fallen forward, depending on his centre of gravity.
Although his view at David Bain's first trial in 1995 was the wound was a contact or close-range wound, he now had to accept the wound was not a tight contact wound, taking into account the marking caused to Robin Bain's skin by the gases expelled from the rifle.
Dr Thomson said he reviewed all the material in the case, including results of test firings of the rifle, and also sat through the main part of Dr Dempster's evidence.
He said the blood spatter on the alcove curtain 820mm above the floor suggested Robin Bain's head must have been "fairly close" to the curtain, although he could not be precise as he was not a spatter expert, but he thought "within a foot [305mm]".
He was unable to say at what height the blood and other material had exited the entry wound, but it would have happened "within milliseconds" of the bullet entering because of the increase in pressure in the skull. And if Robin Bain had been standing, he would have collapsed during the next one or two seconds.
Asked which way he thought Robin Bain would have fallen if he had been leaning over a chair, Dr Thomson said it was difficult to speculate. He thought that calculation was "beyond anyone's expertise".
And, while one would think a person in such a position would fall forward, the concussion of the bullet could cause them to fall backwards.
As for the range from which the bullet was fired, he agreed with Dr Dempster it was an intermediate wound where there was no "searing", but where there would be some particles.
And, based on the results of test-firing of the rifle by police armourer Robert Ngamoki and ESR tests using pigskin, he felt that particles of unburnt powder suggested the rifle was "some centimetres" away from Robin Bain's head. It could have been 16cm, 18cm or 20cm away, he said. It was not a "near contact" wound like that on Laniet Bain's left cheek.
Robin Bain's wound was fairly regular looking, so the weapon would have been held at close to right angles to the head, Dr Thomson said.
Asked whether a small splash of blood on the nail of the little finger of Robin Bain's left hand would have been back spatter from the wound to his head, the witness said it would not have been if Robin Bain had been using his left hand to shoot himself.
But if his left hand was up near where the shot went in, it could be back spatter. He was not an expert on back spatter "or any other kind", though he had "seen a bit", Dr Thomson said. The fact there was a silencer on the rifle meant some of what came back from the wound would be absorbed in the tube of the silencer if the rifle was close enough.
The shot which killed Margaret Bain had an entry wound directly above the left eyelid, the bullet travelling backwards and causing several fractures. Death would not have been instantaneous, as there was evidence of a degree of bruising into the upper eyelid and blood in the lungs, meaning Margaret Bain had continued breathing for a time.
The rifle had been almost immediately above her and the wound was a near contact rather than contact wound, as there was no evidence of "searing".
Dr Thomson said he agreed with Dr Dempster the wound to Arawa Bain was not a contact or near contact wound. She had been shot in the right forehead, the direction of the wound being "pretty much backwards, parallel to the axis of her body".
Neither did the wound have any of the soot, searing, burning or powder grain evidence which were features of "intermediate" wounds. It was a distant wound which could have been caused by a shot from "as far away as two feet [61cm] or a lot more".
But, in the case of Laniet Bain, who had three gunshot wounds to her head, Dr Thomson said whoever killed her had pushed the rifle firmly down on top of her head before firing what would have been a fatal shot. His reason for believing it was a "hard contact" wound was the bruising to the scalp and the larger size of the entry wound.
The effect of the hard contact was that the gas "and everything" from the rifle would go in through the wound, which was why it was different from the two other wounds, one to the left cheek, the other above the left ear, Dr Thomson said.
He believed the initial wound was the one to the cheek. It was a fairly close range shot and "was not going to be fatal". Laniet would have continued to breathe, although, with such an injury there would almost certainly have been a period of unconsciousness resulting from the force of the initial impact. But the unconsciousness would have been relatively brief.
It was reasonable to assume that, at some stage after the shot to the cheek, Laniet got herself up from the position in which she was finally found - "the direction of the blood travel could indicate that, but I'm not a blood spatter expert", Dr Thomson said.
He told Crown counsel Cameron Mander the "other issue" which had puzzled everybody was how anyone could get behind Laniet to shoot her in the top of the head. He believed the subsequent shots were fired when Laniet was in a half sitting position on her bed.
The blood from the initial wound would have accumulated in the back of her throat, making breathing quite noisy. He was aware she had inhaled some blood into her lungs.
That would have happened while she was still breathing, but not later, and any blood that continued to trickle would accumulate passively in the back of her throat. On the question of Laniet Bain being heard to gurgle, Dr Thomson said she must still have been alive and making some form of respiratory effort for that to happen.
He agreed with Dr Dempster that either of the other two wounds was likely to be immediately fatal. Both went through major brain structures and, after either wound was caused, it was "highly unlikely" there would be any continued breathing because of the destruction of important structures in the brain.
Asked by Mr Mander for a comment on the fact there were two fatal wounds, Dr Thomson said, "I guess it's to make sure somebody's dead. Whichever was the second was in my view unnecessary".
Dr Thomson has completed his evidence in chief and will return on Wednesday, when the trial resumes, to be cross-examined.
Evidence will then be heard from the other pathologist, James Ferris, before the case moves on to witnesses involved with fingerprints and testing the rifle.
