We don't enough of the relevant facts yet and some of them are circumstantially contradictory. (Gunshot on 911 tape that followed closely after Zimmerman contacted 911 said he saw the kid who was walking away and he was following him.) If that truly was a gunshot how does that fit into a fight some distance and time away? There was one witness. Zimmerman's neighbor who upon hearing cries for help looked out his window and saw the kid on top of Zimmerman punching or fighting with him. Zimmerman was on his back. However, the witness didn't see the start of the altercation or when they first came together. When they first came together--that's the key point. What happened from that point on. Then after establishing that based upon all available evidence at the scene you work backward on the timeline and to a certain context also in investigating further too.