left for dead
Suppose you've been chased by a maniac who's trying to kill you, and you manage to drop a rock on him so he slides a few yards down the hillside and appears to be either unconscious or dead. Do you (a) just scream a lot and then wander off, or (b) check if he is dead, possibly finish him if he isn't, and take his gun anyway? It might have been an idea if he'd fallen into a crevasse so his intended victim wouldn't have had the (b) option but there was still a possibility of his surviving.
"I beseech ye in the bowels of Christ, think that ye may be mistaken."