Mo. Rev. Stat. § 56.380
It is unlawful for the circuit attorneys or the assistant circuit attorneys of the courts of this state having jurisdiction of criminals within cities in this state having a population of seven hundred thousand inhabitants or more to contract for, directly or indirectly, or to accept, receive or take any fee, reward, promise or undertaking, or gift or valuable thing of any kind whatsoever, except the salary of his or her office prescribed by law, for aiding, advising, promoting or procuring any indictment, true bill or legal process of any kind whatsoever against any person or party, or for aiding, promoting, counseling or procuring the detection, discovery, apprehension, prosecution or conviction of any person upon any charge whatsoever, or for aiding, advising or counseling of or concerning, or for procuring, promoting or effecting the discovery or recovery, by any means whatever, of any valuable thing which is secreted or detained from the possession of the owner or lawful custodian thereof. Any officer who is convicted of the violation of any of the provisions of this section shall be punished by imprisonment by the state department of corrections for not more than seven years and in addition shall forfeit his or her office.
§ 56.380, RSMo