At the hearing the prosecution will have to show way more than they have up till now and the local cops will probably be called in as witnesses (at least deposed) for the defense.
What concerns me the most is how much Zimmerman has been talking to the authorities with no attorney present. Any inconsistency, misstatement or exaggeration will be used to call his version of events in to question.
He could be totally forthright and cooperative, and still say something that puts him in serious legal jeopardy.
The prosecution will have to show cards at the Arthur hearing if they contest efforts to bond GZ out.