Mo. Rev. Stat. § 56.110: If interested in case, court to appoint substitute.

If the prosecuting attorney and assistant prosecuting attorney be interested or shall have been employed as counsel in any case where such employment is inconsistent with the duties of his or her office, or shall be related to the defendant in any criminal prosecution, either by blood or by marriage, the court having criminal jurisdiction may appoint some other attorney to prosecute or defend the cause. Such special prosecutor shall not otherwise represent a party other than the state of Missouri in any criminal case or proceeding in that circuit for the duration of that appointment and shall be considered an appointed prosecutor for purposes of section 56.360.