I'm curious about this myself. I know I'm going to come off sounding like the douche' I am, but I have to ask, if it was so valuable to the gentelman who made it, shouldn't he have kept a (rimshot, please) closer eye on it? Now if it was in his room under lock and key and someone broke in, he took all the precautions he could, he can't be blamed. But if he left it in the open in a crowded room, well, people are unpredictable and impulsive, if someone sees the chance to get away with a nifty piece, they will. He shouldn't be surprised.
You guys remember a few years back when Master Replicas had the collectors society party at one of these cons, and someone swiped one of the only two Luke stunt ROTJ sabers? That actually turned out well as it was returned, but this person I suspect will not be as lucky.