I would personally message him on facebook, being mature in nature about the issue and stating I do not like such comments directed at my girlfriend and that he needs to stop, remove her from his profile and not contact her at school. If he is able to take that with out retorting back in a nasty manor then make sure that your girl is with people at school and is aware of her suroundings. Lots of people have big big mouths online and would wet there pants to think of saying such offline.
If he comes back to you, and is like raging... I would find out where he lives, and then send him a message with his address, color of house he lives in aswell as the color of his naighbors houses on ether sides of him, color and make of cars in the drive way aswell as the colors and make of cars in the nextdoor driveways to his, and what his mailbox looks like.
All colleges have security, makes sure that she has them walk her to and from her car, she is not alone walking around campus and see if he stops messaging her. If not your discression from there.. Thats just my two cents.