There was a somewhat similar case in Tampa where a man (Dontae Morris) murdered two police officers (plus three others) and his girlfriend (Cortnee Brantley) had withheld information regarding his true identity from the police.
She was charged and convicted for violation of 18 USC 4 - "Misprision of Felony", which is defined as follows:
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.