When the LA Police Officers were duly acquitted in the Rodney King case, the Feds couldn't wait to jump in with charges of "denying civil rights," ran them through a kangaroo court, and locked up the cops for many a year. The Feds are 'empowered' to act any damn time they feel like it and don't kid yourself otherwise.
They were acquitted in the state court because a politically motivated prosecutor over reached on the charges -- attempted homicide -- instead of bringing charges for the actual crime -- aggravated assault. The DA could not prove attempted homicide which would have had a 20 year sentence and the jury rightly acquitted. The Feds stepped in afterward with a Civil Rights charge and won conviction. If the state had not over reached and convicted them of aggravated assault, they would have spent more time in the slammer than what they did.