If he is charged, it will be pure 100% political.
Either that, or we'll find out that the evidence released by the Town of Sanford was a misleading selection.
Which I think would be darned difficult to pull off, against the interest of the town, etc. So, don't take my remark as "could be" in any more than an academic sense.
He is going to be charged, and he is going to be convicted. Once he is charged, no juror they impanel will feel or be safe. There will be death threats to the jurors and everyone else involved.
If he's not charged (but he will be), Holder & Company will manufacture a federal offense and come for him.
Zimmerman should be heading for Mexico in the trunk of a car right now if he has any survival instincts.