Hate speech is Constitutionally protected:
Brandenburg v. Ohio
R. A. V. v. City of St. Paul, 505 U.S. 377 (1992)
Speech in advocacy of violence becomes illegal only when it actually incites imminent lawless action. Had the leader of the New Black Panther Party incited a crowd to immediately go to Zimmerman’s home and ‘arrest’ him, then and only then could authorities consider arrest or other legal action.
Obviously the legal community of Central Florida is aware of the statement:
Former Orange-Osceola County prosecutor Esther Whitehead said the Panthers' bounty opens them up to civil and possibly criminal liability.
"I can't see how anyone can go out
and take action as a private citizen without some government action like the issuance of a warrant," she said.
Black Panthers offer bounty for gunman in Trayvon Martin's death
Former prosecutor Whitehead clearly knows the law, until such time as the speech incites imminent or actual action, and remains speech only, that speech is protected.