You are on to something here. I'm guessing that if Zimmerman is acquitted of murder charges, the fed's will fill a civil rights violation against him.
And then Zimmerman will be convicted in a federal court. The Attorney General will see to that.
I suppose that's somehow still possible, but the DOJ already sent FBI agents down to investigate a possible Civil Rights charge, and concluded there was no basis for that. Overcoming their own investigation would be a pretty big hurdle.