Mo. Rev. Stat. § 388.600

Any railroad company may apply to the director of the department of public safety for appointment of one or more of its employees of the age twenty-one or over, who regularly work in this state and who are residents of this state, or of an adjoining state, as railroad policemen for the purpose of protecting the property of the railroad, or property for which it is responsible, and for the purpose of protecting the persons and property of its passengers and employees.