Playing sonic adventure, plot spoilers?
I faffed about in some absurdly generous pinball tables until I got enough rings to fill the casino vault to the point I could take a chaos emerald. Considering the rings were the casino's in the first place I think that's still robbery.
Then a blue Fabergé egg or something descended down a nearby alley, and *then* the emerald gets nicked within minutes of it being in our possession, maybe to hide Eggman's stance on gambling for the time being.