While I think that all of the above posters have offered solid advice, I think that this may be a dangerous situation for your child which warrants an immediate need to change his roommate and, possibly, his dorm.
Dealing with an 18 or 19 year old freshman is different than dealing with an older adult. Any attempt to stand up to a bully–in this case a psycho bully-- with whom one lives can have dangerous results.
Worth noting is that this very well written and constructed post presents an unusual and extreme case.
P.S. OP: It is difficult for me to imagine how switching rooms (and roommates) could make this situation worse.