Mo. Rev. Stat. § 56.510

The circuit attorney of cities that have five hundred thousand inhabitants or more is required to attend inquests held by coroners in cases of death occurring by violence, and which may result in a charge of felony. The circuit attorney shall make an investigation concerning the death and cause to be brought before the coroner any witnesses he desires, and shall be permitted by the coroner to assist in the interrogation of witnesses for the full development of the circumstances leading up to and resulting in the death, and for his information concerning any possible criminal charge that may grow out of the same. For these services there shall be taxed as costs a fee in favor of the circuit attorney of ten dollars for each inquest, to be paid as other costs by the respective cities. Each coroner shall promptly notify the circuit attorney of his city of the time and place of inquisition concerning any death of the aforesaid characteristics.