Here's my take on the issue: I wasn't there that night but we do know Zimmerman shot Martin. Under what exact circumstances? I don't think we are going to know. Dead men tell not tales and Zimmerman is going to have a version that is only going to be corroborated and contradicted by the 911 call , eyewitnesses(if you want to call them that because as far as I know they did not see or hear too much), and the circumstantial evidence.
There is going to be a jury of 12 people. A conviction is going to take all 12 to go against Zimmerman. Zimmerman only needs 1 to find him not guilty by reasonable doubt.
So I think he is going to walk out of this trial either found not guilty(needs 12 to find him not guilty- a bit tough), or a hung jury( no agreement).
If the first case, the state will simply say we tried, blah blah, blah, don't blame us for this travesty of justice. If a hung jury, the state can always try again or not.