Well... there are several forms of therapy that've proven effective with PTSD.
Cognitive therapy is about understanding and changing the way the patient relates to the trauma, while exposure therapy is all about repeating the event through conversations with a therapist. The latter can be difficult at first but the theory is that a flood of bad memories may overwhelm the senses and eventually desensitize the patient until they no longer feel so stressed about the event. It's typically coupled with relaxation exercises.
Certain medications have proved to be effective too, but unless he's willing to go to the wardens with this I'm not sure how helpful that advice is... I think your best bet right now is to talk to him and try to get him to face his problems rather than bottle them up. [ A beat. This isn't necessarily relevant, but it is important.]
Drug- and alcohol abuse is common among sufferers of PTSD. You should keep an eye on his drinking habits.