A criminal ring that had been stealing cars from different parts of Athens and blackmailing their owners into paying for their return was being run by an inmate at Malandrino Prison in central Greece, police said on Saturday after arresting four suspected members of the racket. The four men, arrested in Sepolia, western Athens, are believed to have stolen an undetermined number of vehicles and gathered information about the car owners. According to police, this information was passed on to the convict who telephoned the owners of the vehicles from jail, demanding that they pay 1,000 euros each to secure the return of their cars. Three of the targeted victims paid up, police said. But several others refused and contacted police a few weeks ago, prompting the investigation that led to the arrest of the four suspects.