There is nothing federal about this case. Zimmerman was a neighborhood watch volunteer, not a law enforcement officer. You need “state action” for the basis of federal civil rights violations, and Zimmerman was not an employee of the state or a municipality. Doesn’t seem to qualify as a federal hate crime, and no instrumentality of interstate communication was used to commit or plan the shooting. Interstate transportation doesn’t seem to be part of these facts either, and the shooter, the victim and the shooting site were all located within the same state.
About the only thing the FBI could be looking at would be the actions of the local police in investigating the shooting.
That's where you are wrong. Skittles and all Mars/Wrigley products are manufactured in Gainesville, Georgia; Yorkville, Illinois; or Chatanooga, Tennessee. Trayvon Martin was engaged in interstate commerce when George Zimmerman profiled him as a Skittles and Ice Tea kid and gunned him down. The feds have jurisdiction based on the Commerce Clause - the same clause that gives them authority over everything else they have decided to meddle with. As a special bonus, thanks to the thoroughly bizarre Wickard v. Filburn case, shopping for snacks for his little brother would count as interstate commerce even if Trayvon Martin had purchased Florida orange juice.