What facts? What do we actually know about this case? Correct me if I'm wrong, but my understanding so far goes something like this:
Things we know:
1. Zimmerman pursued Martin against the instructions of the 911 operator.
2. Zimmerman was carrying a weapon.
3. During a confrontation/struggle, Zimmerman fired his weapon and killed Martin.
Things we don't know:
1. Who started the confrontation/struggle (Odds are that Zimmerman did, but "odds are" doesn't get you **** in a trial).
2. (Similar to 1) Who, if anybody, was acting in self-defense.
I think this is a travesty, but if I were a prosecutor I would not want this case showing up on my desk. All Zimmerman would have to show is that he reasonably believed he was in danger of serious injury.