Mo. Rev. Stat. § 540.160
Whenever thereto required by any grand jury, or the foreperson thereof, or by the prosecuting or circuit attorney, the clerk of the court in which such jury is impaneled shall issue subpoenas and other process to bring witnesses to testify before such grand jury. After the finding and returning of any indictment by the grand jury, such foreperson, prosecuting or circuit attorney, or jury, shall not have the right to cause any subpoena or other process to be issued for any person who is known or believed by such foreperson, prosecuting or circuit attorney or jury to be a witness in behalf of the person or persons so indicted, or who has been subpoenaed as a witness in behalf of such person or persons, or who such foreperson, prosecuting or circuit attorney or jury may have reason to believe will be summoned as a witness in behalf of such person or persons, in regard to the matter or matters charged against such person or persons in such indictment, except upon the written order of the judge of the court into which such indictment is returned.
§ 540.160, RSMo