Or, How to Not Get Shot by the Police.
This is an important thing to consider. When a cop is called to a scene where there's been a shooting, he or she will have no idea who the good guy vs. bad guy is. You need to consider this before you hold the bad guy at gunpoint or continue to display your firearm.
Personally, I always think about how I can put away my gun as soon as possible after an event. Back into the holster and concealed is a good way of not having it out where an officer might mistake me as the active shooter. Right or wrong, it doesn't matter when a cop puts a few extra orifices in you thinking you're a threat. While it'd be nice if so many people were openly armed in society that cops don't automatically assume gun = threat, that's not a reality. Better to be hassled for the wrong reasons and alive than right and in a pine box.