The facts as we know them to this point support Zimmerman's version of what happened and the prosecution has the burden of demonstrating otherwise. If you are going to examine his story from the 3 angles of (1) fact, (2) maybe/maybe not, or (3) complete lie, and you can only conclude either 1 or 2, then you have to side with Zimmerman.
The line has been moved so many times with Zimmerman that it's ridiculous. The assumptions and hopes at various times were that the evidence showed or would show that he stalked and killed him in cold blood, that he called him a fucking coon and hated black people, that he killed him execution style (my personal favorite-- thanks RJ), that the angle of the bullet should have been different than it was, that it must be Trayvon screaming because the screaming stops after the shot, that he had no wounds to his head (which now has apparently morphed to them only being superficial wounds), etc... Now it's down to him instigating it by following him in the first place. The line keeps getting moved based upon the preconceived notion that he wrongly killed this kid and needs to pay in some respect. The rush to judgment has made people silly. It has become like a political viewpoint where you take a position and hunker down refusing to budge no matter where the bombs are being dropped.
I was late to reading up on this case, but it seemed pretty obvious to me from the outset that people were getting wound up over a case that probably didn't warrant it. The case has always seemed to me to be a tragic confluence of circumstances.