18 USC § 1119 - Foreign murder of United States nationals
(a) Definition.— In this section, “national of the United States” has the meaning stated in section 101(a)(22) of the Immigration and Nationality Act (8 U.S.C. 1101 (a)(22)).
(b) Offense.— A person who, being a national of the United States, kills or attempts to kill a national of the United States while such national is outside the United States but within the jurisdiction of another country shall be punished as provided under sections 1111, 1112, and 1113.
(c) Limitations on Prosecution.—
(1) No prosecution may be instituted against any person under this section except upon the written approval of the Attorney General, the Deputy Attorney General, or an Assistant Attorney General, which function of approving prosecutions may not be delegated. No prosecution shall be approved if prosecution has been previously undertaken by a foreign country for the same conduct.
(2) No prosecution shall be approved under this section unless the Attorney General, in consultation with the Secretary of State, determines that the conduct took place in a country in which the person is no longer present, and the country lacks the ability to lawfully secure the person’s return. A determination by the Attorney General under this paragraph is not subject to judicial review.