COPENHAGEN, Denmark—A former Guantanamo detainee has been arrested in Denmark on suspicion of withdrawing $18,900 from other people's accounts using stolen debit cards and PIN codes, police said Thursday. Slimane Hadj Abderrahmane, a Danish citizen, was released from the Guantanamo Bay detention center in 2004 after nearly two years in captivity. Abderrahmane, 34, was arrested Wednesday and ordered held in jail for two weeks on preliminary fraud and theft charges, police said. He is suspected of stealing three debit cards—two corporate cards and one personal—and the corresponding PIN codes. Police did not say how he stole them. They said Abderrahmane,...