Mo. Rev. Stat. § 106.090
Immediately upon meeting, the commission shall proceed to organize by electing a president and a secretary and thereupon shall designate some day not less than twenty days nor more than thirty days after the service of the summons for the appearance of the accused and cause a summons to be issued, signed by the president of the commission and countersigned by the secretary thereof, with a copy of the articles of impeachment annexed, requiring the accused to appear on the day designated for that purpose, and answer charges exhibited against him, which shall be served by a messenger appointed by the commission, a reasonable time before the day set for his appearance. The commission shall have power to employ such clerical help and assistants as they may deem necessary to the proper conduct of the trial.
§ 106.090, RSMo