18 U.S.C. § 2243

(a) Of a Minor .— Whoever, in the special maritime and territorial jurisdiction of the United States or in a Federal prison, or in any prison, institution, or facility in which persons are held in custody by direction of or pursuant to a contract or agreement with the head of any Federal department or agency, knowingly engages in a sexual act with another person who— (1) has attained the age of 12 years but has not attained the age of 16 years; and (2) is at least four years younger than the person so engaging; or attempts to do so, shall be fined under this title, imprisoned not more than 15 years, or both. (b) Of a Ward .— Whoever, in the special maritime and territorial jurisdiction of the United States or in a Federal prison, or in any prison, institution, or facility in which persons are held in custody by direction of or pursuant to a contract or agreement with the head of any Federal department or agency, knowingly engages in a sexual act with another person who is— (1) in official detention; and (2) under the custodial, supervisory, or disciplinary authority of the person so engaging; or attempts to do so, shall be fined under this title, imprisoned not more than 15 years, or both. (c) Of an Individual in Federal Custody .— Whoever, while acting in their capacity as a Federal law enforcement officer, knowingly engages in a sexual act with an individual who is under arrest, under supervision, in detention, or in Federal custody, shall be fined under this title, imprisoned not more than 15 years, or both. (d) Defenses .— In a prosecution under subsection (a) of this section, it is a defense, which the defendant must establish by a preponderance of the evidence, that the defendant reasonably believed that the other person had attained the age of 16 years. (e) State of Mind Proof Requirement .— In a prosecution under subsection (a) of this section, the Government need not prove that the defendant knew— (1) the age of the other person engaging in the sexual act; or (2) that the requisite age difference existed between the persons so engaging.