Mo. Rev. Stat. § 545.280: Prosecuting witness, who deemed.

When the information is based on an affidavit filed with the clerk or delivered to the prosecuting attorney, as provided for in section 545.250, the person who made such affidavit shall be deemed the prosecuting witness, and in all cases in which by law an indictment is required to be endorsed by a prosecutor, the person who makes the affidavit upon which the information is based, or who verifies the information, shall be deemed the prosecutor; and in case the prosecution shall fail from any cause, or the defendant shall be acquitted, such prosecuting witness or prosecutor shall be liable for the costs in the case not otherwise adjudged by the court, but the prosecuting attorney shall not be liable for costs in any case.