Surely if he *had* to stick it in the compartment place the train company is responsible for it to some extent. CCTV is usually around on trains as well, if you haven't already, get the police involved, useless as they are it could still be of some help if they think it's likely they can find the dickwad who nicked the bike.
I'm scared shitless of black guys in tracksuits, it sounds so bad when I say it but I really am. They always seem to go around in pairs and look you up and down al the time as if they're sussing wether you're worth robbing or not. :-