Okay let's say that's exactly what happened.. do you think the people that kill people so flippantly leave loose ends? If you're the trigger man you've got to know you are sealing your own death warrant by being involved at all. This isn't the John Wick universe hired killers are a dime a dozen and being expendable is a feature not a bug. So whoever murdered that man is probably occupying an unmarked grave in the hills outside Terlingua.