a) There's a case that decided the police are not under obligation to protect you. (I'm not sure which jurisdiction this was at, or if I'm properly reading it, but that is my understanding of it.)

b) I've heard the argument that if you are going to use deadly force, you should not fire a warning shot or anything, and just go ahead and kill them. Otherwise you didn't really believe you were actually in immediate danger. (This is probably from Texas law.) Commentary on that? (Or perhaps it is just in the hopes that the person you shot dead can't sue you for hurting them and that any next of kin won't bother.)