The blood ring comics

Well... that's one reason. Ask me, he would have many reasons not to kill Bryan without a second thought (not that he wouldn't have the right to...).

The main reason, no matter what, is that it is never easy to take a human life. Not even from one who's already labeled as "dead". (At this point, Bryan would tap my shoulder and say; "Hey, don't label me! Do I look like a can of soup!?" :D)