Where i come from that is absolutely not true. You arent held to 20 20 visiok of hindsight. You are held to what a reasonable person would do. Although thats extremely subjective, Im positive you would not be considered excessive for killing a man walking into a club with an ak47 just because you dont "know" what his intentions are or if its real, loaded etc. All anyone can do is act based on the information they have and then apply some critical thinking. If we as citizens, or police ofcrs were held to a standard of acting strictly off what we know...then we would simply not be able to survive in dangerous situations.