As hot and as bad as that fire was, it’s doubtful there were any hands left on the corpse; just arm stumps. I’ve seen pics of victims of that kind of burning, and it ain’t pretty and sometimes, hardly discernible as a human’s remains. Just awful.
The fire was necessary to destroy all the computers that he had with him. He had more than a dozen in the car. Shooting or poisoning Hastings would have left the evidence on the ocmputers. Two birds - one stone.
I expect some of Hastings’ friends to die strangely soon. He most assuredly hid some of the ‘big story’ with others.