I have been in this situation a few times and have never had to had to actually kill someone thankfully but I have been scary close on more than one occasion. It is extremely difficult in the heat of an altercation to think about “dead men tell no tales.” You should also consider that if you commit to pulling the trigger to shoot in one string until you are certain the threat is neutralized/dead. With today’s investigation techniques if you “finish” someone off after the fact it will come out and you will be in far worse shape than dealing with a discrepancy of events.