Mo. Rev. Stat. § 86.543

86.543. Pension shall be paid after twenty years of service in certain cases. — If any member of the police department of any such city, who shall have served faithfully twenty years and less than twenty-five years in such department of which the last six years shall be continuous, be removed, suspended or discharged from such department, or become or be found upon examination by a medical officer selected by such board and authorized by said applicant to be superannuated, by age, permanently insane or mentally incapacitated or disabled physically or mentally so as to be unfitted or unable to perform full police duty by reason of such disability or disease so as to render necessary his retirement from service in such department, if the said board of trustees find such incapacity does not result from misconduct on the part of such member, it shall pay to the said member from said pension fund, a sum equal to four-fifths of one-half the average monthly rate of salary which such member shall have received on said force during three years immediately preceding the date of his retirement. After the decease of such member, his wife while single, and children under sixteen years of age, if any survive him, shall be entitled to the pension provided for in sections 86.510 to 86.577 .

(RSMo 1939 § 9484)