Could it have at all been possible that he was acting in self defense? Or that, at the very least, it wasn't 2nd degree murder? The jury thought so. I'm of the opinion that they know more than us so I'd stand by their decision.
Acquittal just isn't the same as innocent. Experts studying the case are saying there didn't seem like enough evidence to convict the man.
I am pretty sure that burden of proof would have been extremely difficult, given the conflicting reports Zimmerman gave over numerous interviews.
In addition, the interview yesterday with one of the jurors suggests that they wanted to convict him of a crime but could not fit the case into the two charges they were allowed to use. It is not a matter of not enough evidence, it is a matter of flawed laws which give more legal rights to the killer than the victim.