Wow! What a conversation! We had a lawyer who represents the local PD at our monthly meeting last month. I believe it would depend on time and locale as to what you would have time to do. If we had the shooter down, we call shooter down, we then call 911 to let them know that the threat had been neutralized and explain what we were wearing.
This is a hot mess and you could be shot because you have a firearm and they are looking for a "bad guy" with a gun...you just happen to be a "good guy" with a gun. At this time they do not know that. Be safe, be careful! Do what they ask!! Do not let them get that 3913/3906/4566/.45 Shield! Oh, those are what I may have on me depending on the weather.