Missouri state law is if you are in any part of the intersection when the light turns red you can be cited. As a general rule for most officers, if you are past the white "stop" line prior to it turning red you are good to go.
Get an attorney and get it knocked down to a non moving violation so it won't hurt your insurance.
Funny fact: intersections that have the red light enforcement by cameras have higher instances for rear end collisions after the cameras and signage are installed because people tend to stop abruptly when the light turns yellow.