Read this in a short story: "I have called to see you upon a subject which I am sure will enlist your keenest interest, for several reasons. It relates to a magnificent jewel; it concerns your intimate friends; and it is a problem requiring the most analytical qualities of the mind in its solution."
Actually, the only thing that wasn't stolen at the Louvre's Apollo Gallery is the Regent Diamond, figure no one would take it because something to do with a curse.
I've also found that the two thieves were leaving for Algeria, thanks of a trace of DNA evidence recovered from a helmet and their past in burglary cases according to the police.