You didn't specify whether you are the shooter, so I have two answers. If I'm the shooter I won't be 'stopped', I'll be the one calling 911.:P
"What's your emergency"
- I was attacked by a man/woman/child/animal and I was so afraid for my life that I had to shoot. Please send a cop and an ambulance.
If I'm a witness, and I'm stopped for questioning, it will be more like this:
"Can you tell me what you saw?"
- I'm still a little shook up, officer. I want to help, but I need to calm down and talk to my lawyer first. Can I get your card or some other way to get in touch with you? Am I free to leave?