Dear Kiss_Alive:
I understand the concept at work in your theory that someone would say something. But why would someone say something about an unknown person getting into a suitcase that they don't know ISN'T that persons. Nobody will know who's luggage is who's. Especially the conductor, who changes fairly frequently. The best bet would be the owner of the bag waking up, or the car attendant noticing (because the CA is there for the whole trip). But besides that, on a Superliner, on could go downstairs to the luggage racks and "raid" that. Same on an Amfleet carriage one could simply go to the back of the car and "look" for their luggage, and takes somebody else's stuff. I know I would be too unsure of ownership, asides from my own stuff, to say anything to someone getting into a piece of luggage. If I was very suspicious I would report it to the attendant or conductor, but without any way to confirm the ownership in the first place I would have nothing to base my suspicion on.
Anyway,
Regards, Logan