It would rise to a Federal crime only if the NBPP snatches him and transports him across a state line. If they're really that stupid as to illegally detain Zimmerman and keep him in Florida it would only be a breaking the state law.
I think it's interesting that they can publically offer a "reward" for Zimmerman's "capture" and not run afoul of vigilanty laws or Posse Comitatus.
As I said in my earlier comment, couldn't just making that announcement get them arrested on conspiracy/ incitement charges?
btw, although most of ChairmanAgnostic's post was of course a total crock (He claims that "Teabaggers" were behind it, even though the NBPP was around at least a couple years before the Tea Party movement began) and just the usual "Agents provocateurs" BS that the Dummies and other ultra- leftists use whenever one of their own goes nuts, he did unwittingly hit on a good point:
"I doubt that reall black panthers would be so transparently stupid."
That actually is near enough to the truth, but not in the way the DUmmy thinks (Considering it evidence that the NBPP was brought about as part of some big conspiracy by the evil neocons). Many of the original members of the Black Panther Party are not exactly big fans of the NBPP, the two groups actually are not technically affiliated with each other. It's sort of like how Fred Phelps' cult is called the Westboro Baptist Church, even though it is not connected to any of the official, recognized branches of the Baptist Church.
The original Black Panthers may have been radicals, but even they can see that the NBPP are a bunch of psychotic wannabes whose views are too extreme even for them.