Mo. Rev. Stat. § 546.740: Execution, witnesses.

The chief administrative officer of the correctional center, or his duly appointed representative shall be present at the execution and the director of the department of corrections shall invite the presence of the attorney general of the state, and at least eight reputable citizens, to be selected by him; and he shall at the request of the defendant, permit such clergy or religious leaders, not exceeding two, as the defendant may name, and any person, other than another incarcerated offender, relatives or friends, not to exceed five, to be present at the execution, together with such peace officers as he may think expedient, to witness the execution; but no person under twenty-one years of age shall be allowed to witness the execution.