Mo. Rev. Stat. § 490.530

Any such affidavits, taken out of this state and in the United States, may be taken before a notary public, or before any associate circuit judge, and when taken before such associate circuit judge shall be accompanied by a certificate of the official character of such associate circuit judge, attested by the seal of state, or proved by the certificate and seal of the clerk of the same court of record in the state where the affidavit was made, certifying that such associate circuit judge had full power and authority to administer oaths at the time such affidavit was taken, and that the signature of such magistrate thereto is genuine.