Zimmerman said he was attacked by Martin while he was returning to his SUV. Obviously, you don't believe him. Do you have any proof to the contrary. Isn't it up to the state to prove that Zimmerman is lying? How does Zimmerman prove that Martin attacked him?
Check out this video that speaks about corroborating witnesses
That's the key, isn't it? It may very well be that Zimmerman committed a crime - but I have seen no evidence that could prove it. There is only one known witness who can testify to who started the fight, and that is Zimmerman.
You don't even have to believe Zimmerman is innocent to believe that he should not be prosecuted...