The federal definition is in 18 U.S. Code § 4 is
"Whoever, having knowledge of the actual commission of a felony cognizable by a court of the United States, conceals and does not as soon as possible make known the same to some judge or other person in civil or military authority under the United States, shall be fined under this title or imprisoned not more than three years, or both."
While this may potentially be used against state/local officials who overlook crimes by government actors, it may be very difficult to get a federal indictment.
