Missouri Revised Statutes Title XXXVII. Criminal Procedure § 545.380. Defense witnesses--commission to take deposition, when

When any issue of fact is joined in any criminal case, and any material witness for the defendant resides out of the state, or residing within the state, is enceinte, sick or infirm, or is bound on a voyage or is about to leave this state, or is confined in prison under sentence for a felony, such defendant may apply to the court, or judge thereof, in which the cause is pending, for a commission to examine such witness upon interrogatories thereto annexed, and such court may grant the same upon the like proof and on the like terms as provided by law in civil cases. The court, or judge thereof, granting such commission, may permit the officer prosecuting for the state to join in such commission. The deposition of any witness confined in prison under sentence for a felony shall be taken where such witness is confined.