Mo. Rev. Stat. § 545.720
A motion to continue a cause on the part of the defendant on account of the absence of evidence must be supported by the oath or affidavit of the defendant or some reputable person in his behalf, showing the materiality of the evidence expected to be obtained, and that due diligence has been used to obtain it, and where the evidence may be; and if it is for an absent witness, the affidavit must give his name, and show where he resides or may be, and the probability of procuring his testimony, and within what time, and what facts he believes the witness will prove, and that he believes them to be true, and that he is unable to prove such facts by any other witness whose testimony can be as readily procured, and that the witness is not absent by the connivance, procurement or consent of the defendant, and what diligence, if any, has been used in the premises by the defendant, and that the application is not made for vexation or delay merely, but to obtain substantial justice on the trial of the cause.
§ 545.720, RSMo