Not reporting such felonies, is itself a felony
18 U.S. Code § 4 - Misprision of felony
US Code
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.
(June 25, 1948, ch. 645, 62 Stat. 684; Pub. L. 103–322, title XXXIII, § 330016(1)(G), Sept. 13, 1994, 108 Stat. 2147.)