Mo. Rev. Stat. § 544.150: Reward by county commission.

Whenever the county commission of any county in this state, or any two commissioners thereof in vacation, shall be satisfied that any felony has been committed in said county, such commission or commissioners may, at their discretion, offer a standing reward of not exceeding five hundred dollars for the apprehension and arrest of the person or persons committing the same, which reward shall be paid out of the county treasury; but in no instance shall any reward, or any part thereof, be paid to any person who may be entitled thereto until final conviction of the defendant.