As an armed citizen who doesn't wear a uniform (Boy Scout uniforms don't count), my thought process is this...
1. Police will be sent to the scene of most shooting with information of it being a "man with a gun" or a "active shooter." call.
2. I am, at that point, a man with a gun at the scene.
3. How do I avoid being shot by responding officers?
My thought is that if I have fired, hit the bad guy, and the threat is down and disarmed, I might just want to holster up, get on my phone with 911, and start screaming my description to the dispatcher in hopes that description is shared with officers so they know I'm not the bad guy.
If I'm at the scene of an active shooter situation, I'm not hunting the shooter down. I'm hiding/covering my family. Maybe when I hear the sirens, I consider holstering up so I don't look like the bad guy when the first responders run in.
If the threat is still active and I am armed and engaging when cops arrive... God help me.