Mo. Rev. Stat. § 491.170: Witness attached, may be discharged on bail.

When a writ of attachment, authorized by section 491.160, shall be executed, the sheriff or other officer shall discharge such witness, on his entering into a recognizance to the state of Missouri, with sufficient security, in the sum of one hundred dollars, which the officer executing the writ is authorized to take, conditioned for the appearance and due attendance of such witness according to the exigency of such writ.