Alexander Dempster said he had never seen a self-inflicted gunshot wound which was "even close" to the trajectory of the wound in Robin Bain's head. He concluded it was unlikely the wound was self-inflicted, but could not exclude the possibility.
Dr Dempster was giving evidence on the 21st day of the retrial of 37-year-old David Cullen Bain who, the Crown says, shot his mother, Margaret, sisters Arawa and Laniet and younger brother Stephen and then his father, Robin, making that shooting look like suicide.
Bain denies the charges, his claim being he returned from his early morning paper round and found his family dead.
The defence case is Robin Bain committed the four murders before turning the gun on himself.
And the question of the angle of the bullet track through Robin Bain's head and whether he could have shot himself with the Winchester .22 rifle made longer than normal by a silencer, was an important aspect of Dr Dempster's evidence, yesterday.
The bullet entered Robin Bain's skull through the front of the bone in the temple area. It then travelled diagonally backwards across the base of the skull at a 45-degree angle and about 5 degrees to 8 degrees upwards.
With wounds self-inflicted using firearms, the general pattern was that in most such wounds to the temple, the bullet passed more or less across the brain, "pretty much at right angles to the front-to-back axis", Dr Dempster said.
Others were inflicted through the forehead from front to back, or upwards and backwards through the mouth or through the skin under the chin.
While the location of the wound to Robin Bain was not "out of court" for a self-inflicted wound, it was at the front end of where such a wound would be expected.
In the course of his evidence, Dr Dempster used the rifle with a mannequin and helmet to demonstrate to the jury the unusual way Robin Bain had to have held the rifle if he shot himself, as the defence claims.
He was the same height as Robin Bain at 1.75m and had a similar arm span of 185cm, although a bespoke tailor whose evidence was read to the court on Monday put Robin Bain's arm span at 185cm-190cm. A steel rod through the line of the bullet trajectory in the model was inserted into the barrel of the rifle so Dr Dempster could carry out his demonstration.
Holding the rifle at the required angle to his head, he had difficulty accessing the trigger because the silencer on the weapon obscured his view. He had to feel around for the trigger guard. Using his right hand, he was well short of the trigger guard.
"For me, it's impossible to fire the gun with my right hand," Dr Dempster said. He was right handed.
It was very difficult to hold the rifle in the upright position because of its weight, he said. Holding the gun with his right hand at the barrel end, he could reach the trigger with the tip of his left middle finger and could have activated the trigger with his left hand.
But it was difficult to do because he could not actually see the trigger and had to "grope along the gun" to feel the trigger guard and then push the trigger.
The witness said he had not sampled a spot of blood on one of the fingernails of Robin Bain's left hand because it was too small for testing at that time. But he said if he had been using his left hand to activate the trigger, it did not make a lot of sense for the blood splatter to have landed there.
Dr Dempster said another factor making it unlikely the wound was self-inflicted was that Robin Bain had been wearing a hat, a green beanie, which was in the hood of his dark blue sweatshirt where he lay on the floor. He had never come across anyone who had shot themselves in the head while wearing a hat, the witness said.
The main reasons he concluded the wound was unlikely to be self-inflicted - although he could not completely exclude the possibility - were the trajectory of the bullet and the difficulty of accessing the trigger with the rifle held in the position required to achieve that angle, Dr Dempster told the court.
He continues his evidence under cross-examination today in the trial before Justice Graham Panckhurst and the jury.
