Prof John Harbison yesterday told the inquest into the death of Mr Richard Barron that the most likely cause of his fatal head injury was a moving object, most likely a motor vehicle.
The State pathologist based his conclusion on his detailed examination of the skull of Mr Barron, a cattle dealer, of Raphoe, Co Donegal, following his exhumation last July.
While Mr Barron's death was initially thought to have been a hit and run, it quickly became a murder inquiry, which in turn resulted in the biggest investigation into the gardaí in the history of the State.
Prof Harbison told the coroner, Mr John Cannon, in Letterkenny yesterday that he found nine to 10 scuff marks on the bone surface at the front of the skull where the skull was fractured. His report stated that the point of impact of the force causing this fracture was one inch above the brow, the point where the scuff marks were deepest.
No such marks were found on the multiple fractures on the left hand side at the base of the skull.
He added that the marks on the skull bone would not have been easily visible at the time of the injury or of the original post-mortem which was carried out by Dr David Barry in Letterkenny General Hospital in October 1996, because of overlying soft tissue.
The inquest jurors were shown photographs of Mr Barron's wounds taken on the day he died and photographs of the injuries to the skull taken by Prof Harbison showing the scuff marks.
Both Prof Harbison and Dr Barry had concluded that Mr Barron died as a result of laceration of his brain and fractures of his skull.
Describing Mr Barron's injuries to the inquest, the Y-shaped wound and fracture to the front of the head and the fractures to the skull base, Dr Barry also cited the soft tissue injury to Mr Barron's little finger on the left hand and injuries to the back of his hands.
Dr Barry described these findings as "most unusual" for a road traffic accident and "more likely to be due to a blow from a blunt instrument".
Prof Harbison, questioned about Mr Barron's hand injuries, said it was possible he could have seen a vehicle coming towards him and reached out to fend it off.
He added that was only one explanation and that the hand injuries could have been from contact with the ground or possibly from a defensive movement.
The inquest continues today with assistant State pathologist, Dr Marie Cassidy, due to testify.