His evidence differed from an opinion by another witness, Dr Alexander Dempster, who has said that the wound would have been caused by a "contact or near contact" shot from the .22 rifle.
Dr Kenneth Thomson gave his view today, on the 23rd day of the retrial of David Cullen Bain in the High Court at Christchurch on charges of murdering five members of his family at their Every Street, Dunedin, home in June 1994.
He was giving evidence of a review of Dr Dempster's post mortem examination, from photographs and notes.
He said blood spatter and brain matter from Robin Bain's wound was at 820mm above the floor, on the curtain to the alcove in the room where he was found. The droplets were big so his head would have to be fairly close to the curtain - within 30cm to 60cm - at a higher level from where the spatter started.
Shock waves through the brain would have caused immediate unconsciousness and collapse.
His opinion was that in photographs of possible suicide positions with the rifle presented by the defence, the person would have fallen forwards as the head was leaning forwards in all of them. Robin Bain was found on his back.
He said the wound had no burnt or seared area with powder particles in it, suggesting it was an intermediate range shot rather than a near contact wound.
He said the rifle could have been fired from 16cm to 20cm away.
Dr Thomson said the post mortem showed that Robin Bain had 400ml of urine in his bladder, which was a normal overnight collection.
The trial, before Justice Graham Panckhurst and a jury, finished for the day late morning so that further inquiries could be made before the defence's cross-examination begins, when the trial resumes on Wednesday.
