I think this is an awesome question. If there is no risk of legal risk, you might actually get an answer here.
Im sure there are those here that have used deadly force (many times in the capacity of their job, i.e. military or law enforcement). Sadly, sometimes this forum has become a breeding ground for critisism, and if a subject like that can be approached with respect, hopefully those that can help us all learn a lesson from a firsthand experience can share.