so we dont know who started the fight, zimmerman said trayvon did...nobody can disprove it
but we can prove that one man chased another.
that might be enough for the jury to declare he started it.
If I'm walking thru your town with a handcannon, i spot you, and i chase your ass 2 blocks into an alley... then i claim i offered you movie tickets and you punched me so i blasted you...
well, i belong in prison for being full of shit and for chasing you two blocks with a gun.
so yeah, 'no witnesses' kinda flies out the window when one dude chases another to a secluded area. By your logic, I can take my date to the woods and rape her because "there were no witnesses... true I dragged her kicking and screaming to the woods, but TECHNICALLY you didn't see it, when I then refused sex and she forced herself upon me..."