Mo. Rev. Stat. § 85.620

The police of the city may be appointed in such numbers, for such times and in such manner as may be prescribed by ordinance. They shall have power to serve and execute all warrants, subpoenas, writs or other process, and to make arrests in the same manner as the marshal. They may exercise such powers in areas leased or owned by the municipality outside of the boundaries of such municipality. The marshal and policemen shall be conservators of the peace, and shall be active and vigilant in the preservation of good order within the city.