Seriously, I have to agree with Scubie.
We had a shooting downtown in Seattle ( have you SEEN how trigger happy and over reactionary our guys have been lately ) a few months back. This was before the woodcarver, but AFTER the girl "getting punched in the face" issue and after the girl getting beaten half to death in the subway tunnel.
Guy was carrying, badguy was acting all tough, pushing people around, trying to intimidate and got in citizen's face. Shoved him, started to beat on him after words were exchanged. Citizen pulls weapon and puts bad guy down hard ( Someone call 911 and get EMT en route please ).
I am not sure if he did any CPR or anything like that, but I do know he did not flee the scene, make any calls or anything like that. I presume he was in shock. When Seattle PD arrived the citizen had sat down on the curb, locked the slide open on his weapon and had it setting on his shoes with his head in his hands. When the officer arrived and asked what happened he very clearly stated he was the guy the cops were looking for and that he had shot the guy in question. No muss, no fuss.
I do not believe he was even taken into custody, and no charges were ever filed. The thing is in how he acted and how he responded when the police arrived.
Now, if he was still in "on" mode and was swinging his pistol from side to side, refusing orders, posing a "threat" I can see the situation going a bit differently.
As Dave Chappelle once famously illustrated (NSFW - look it up), when confronted by the Police, don't be a afraid to do as you are told and STFU.