James T. -- who has a string of previous convictions -- confessed to the criminal court in Basel that he had wanted to steal something valuable from the renowned Basel jewel fair, online news site 20 Minuten reported.
He said he had felt compelled to steal the diamond valued at 220,000 francs ($230,440) as it would enable him to pay off hefty gambling debts.
James T. told the court that he had drunk half a bottle of champagne and some beer before he attended the jewellery show in order to give him enough confidence to go through with his plan, the newspaper reported.
Having dressed well for the show, he identified his intended victim and then feigned interest in his most expensive diamond. As a decoy, he pretended to be angry about something and slipped one of the diamonds into his pocket.
The experienced jeweller soon noticed the missing stone and immediately alerted the police, who traced James T. back to his hotel room. There the police found more diamonds and fake business cards.