Mo. Rev. Stat. § 21.400: Subpoenas shall be issued — attested, how.

Subpoenas for witnesses and the production of records shall be issued at the request of any member of the senate or the house of representatives, or the party accused, or any member of any committee; and all process awarded by the senate or house of representatives, and subpoenas and other process for witnesses whose attendance is required by either the senate or the house, or before any committee, shall be under the hand of the president pro tem, or the speaker and attested by the secretary or chief clerk, as the case may be, and shall be executed by the sergeant at arms of such house, or by a special messenger appointed for that purpose.