I remember seeing the pictures and X rays.
It didn’t appear to be a bullet hole, not to get too graphic, but the brain appeared to be intact which it wouldn’t be had a bullet entered the brain.
It was also in an odd place, top of head not back or side, for a bullet.
It appeared to be from a sharp object. Just a guess but I would say it was from the fire axe.
Actually it was perfectly round and just about .45 inch. The bone was visible in the x-ray and was an intact circle as well leading to speculation that it was caused by an implement used to slaughter livestock that actually punches a hole in the skull and into the brain.