(a)  Offense.⁠—A person who, while confined in a Federal correctional institution under a sentence for a term of life imprisonment, commits the murder of another shall be punished by death or by life imprisonment.

(b)  Definitions.⁠—In this section⁠—“Federal correctional institution” means any Federal prison, Federal correctional facility, Federal community program center, or Federal halfway house. “murder” means a first degree or second degree murder (as defined in section 1111). “term of life imprisonment” means a sentence for the term of natural life, a sentence commuted to natural life, an indeterminate term of a minimum of at least fifteen years and a maximum of life, or an unexecuted sentence of death.