Blood spatter patterns can tell a trained forensic tech loads of data. Like who was on top of who. If Zimmerman shot Martin while Martin was on top of him Blood Spatter from the gunshot can show their relative positions because of directionality of the blood drops. Then there is Gun Shot Residue which can tell how close the shooting victim was to the gun when he got shot.
None of that evidence has been released yet and probably won't unless there is a trial.
The independent investigator may choose to release the evidence, to provide credibility to a no bill decision.