A British woman reported to police that her purse had been stolen in a Marbella restaurant.
Police stopped a car later in the day with four men inside, all with criminal records. The tourist's purse was found in the car. All four men were detained.
One officer saw one of the suspects put his hand to his mouth. That suspect was taken to a hospital to be X-rayed, revealing the diamond in his stomach.
The Associated Press contributed to this report.