If you send him a certified letter (return receipt requested) and request that he return your Xbox immediately or send you the money, you can take a copy of that letter and the return receipt he signed to your local police department and file charges with them for "theft by conversion." A visit by the police, handcuffs, booking photos, etc., will get his attention (and hopefully your Xbox back). I had a former roommate move out and take some of my stuff when she left. Needless to say, I gave the police her work address to pick her up.