Mo. Rev. Stat. § 492.130

The commission shall authorize such officer to cause to come before him such person or persons as shall be named to him by the party suing for the same, and shall command such officer to examine such person touching his knowledge of anything relating to the matter in controversy, and to reduce such examination to writing, and return the same, annexed to the commission, to the court wherein or the associate circuit judge before whom the action is pending, with all convenient speed.