The distinction hinges on whether or not Zimmerman obtains a finding of "immunity from prosecution," which, at this point, has to come from a judge. The immunity is supposed to prevent arrest, detention, and all form of prosecution. But Zimmerman has been arrested and detained, and is being prosecuted.
If the case proceeds to trial, and he is acquitted by the jury on self defense grounds, then he does not have immunity. But, if he wins a Motion to Dismiss on the basis that his use of deadly force was justified, then he is immune from civil suit. Holder can still charge him, but that would be a more bogus charge than the one Corey has applied, because Holder has to allege the reason Zimmerman shot Martin was racial animus.
no, just because the case is dismissed in the criminal court has nothing whatsoever to do with civil liability. Totally different standards of proof. Immunity from criminal prosecution is something granted by the prosecution in exchange for testimony.