Possibly a suicide with the gun being held in the left hand and aimed into his mouth blowing out the side of his head. The hole looks like an exit wound to me because of the irregular shape. It could also be that he was shot from the other side of his head with a gun that was held up against his skull. The energy from it would make a relatively small entry hole if he were shot through the ear canal. But the gasses exploding from the gun directly into his head could cause a large exit hole. This is just speculation based on the observation that the brain matter laying beside him appears to be all that was left intact. The rest was probably blown out of his skull.