Mo. Const. art. VI, § 13

All state and county officers, except constables and justices of the peace, charged with the investigation, arrest, prosecution, custody, care, feeding, commitment, or transportation of persons accused of or convicted of a criminal offense shall be compensated for their official services only by salaries, and any fees and charges collected by any such officers in such cases shall be paid into the general revenue fund entitled to receive the same, as provided by law. Any fees earned by any such officers in civil matters may be retained by them as provided by law. [Effective - 27 Feb 1945 , see footnote]