10 U.S.C. § 825a

(a) In General .— In a case in which the accused may be sentenced to death, the number of members shall be 12. (b) Case No Longer Capital .— Subject to section 829 of this title (article 29)— (1) if a case is referred for trial as a capital case and, before the members are impaneled, the accused may no longer be sentenced to death, the number of members shall be eight; and (2) if a case is referred for trial as a capital case and, after the members are impaneled, the accused may no longer be sentenced to death, the number of members shall remain 12.