Hypothetical situation: Frank pulls out a gun, points it at Bob and demands his wallet. On lookers call the police saying some guy has a gun and is robbing someone. Bob disarms Frank. The police show up... Now the police think the Bob is the bad guy, he has the gun.
Same thing happens without the gun. Some guy attacks you, police are called on a guy assaulting someone else. You break his arm defending yourself. The police show up. Who was the aggressor? You are both going to point at the other guy.
I tell people, if you defend yourself and injure the other guy... run away to safety. (you don't need him to pull the gun you didn't know he had or for his friends to show up) Then you call the police and state:
- I was attacked. (when, where, how and by who)
- I was afraid for my life.
- I defended myself, he may be hurt.
- I ran away, you can find me at this location.
You need to frame the scene for the police who will show up. Most places will allow you to defend yourself with force, if you are afraid for your life. If you claim you were afraid, but you are still standing there flexing* when the cops show up... its not to convincing. A good piece of evidence that you were afraid for your life, is that you ran away from the danger, as soon as you could and you called the cops.
If I defended myself with a gun, then I change number 3 above to: I shot him. Then I add step 5: I need to speak to my lawyer now.
The idea is to be the first to report to the police. Report that you were attacked, you feared for your life, you took actions to defend yourself resulting in the injury to the other guy, and that you retreated to safety as soon as you could.
Sure, there are a ton of cell phones around and someone probably has video. But, how long did it take for them to get the camera out and start recording? Its probably a good bet, that the missed the part where the bad guy pull a knife on a little kid. The also missed the part where you expertly kicked the knife out of the bad guy's hand. (this is probably what caught there attention) By the time there camera starts recording, they get you punching him in the face, then breaking his arm. If they then get video of you running away to safety, the have record of your calling right after to report things line up.
* I realize that the flexing part was a joke... just helped to illustrate.