18 U.S. Code § 1121 - Killing persons aiding Federal investigations or State correctional officers
(a) Whoever intentionally kills—
(1) a State or local official, law enforcement officer, or other officer or employee while working with Federal law enforcement officials in furtherance of a Federal criminal investigation—
(2) any person assisting a Federal criminal investigation, while that assistance is being rendered and because of it,
shall be sentenced according to the terms of section 1111, including by sentence of death or by imprisonment for life.
(1) Whoever, in a circumstance described in paragraph (3) of this subsection, while incarcerated, intentionally kills any State correctional officer engaged in, or on account of the performance of such officer’s official duties, shall be sentenced to a term of imprisonment which shall not be less than 20 years, and may be sentenced to life imprisonment or death.
(2) As used in this section, the term, “State correctional officer” includes any officer or employee of any prison, jail, or other detention facility, operated by, or under contract to, either a State or local governmental agency, whose job responsibilities include providing for the custody of incarcerated individuals.