Saudi police are investigating the origins of a hoax that had hundreds of people believing that old sewing machines may bring fortune because they contained an elusive, and probably mythical, substance known as red mercury.Saudi newspapers on Tuesday published pictures of Saudis proudly posing next to old sewing machines awaiting prospective buyers at traditional markets.The English-language Saudi Gazette newspaper said some buyers were willing to pay up to 200,000 riyals ($50,000) for an old Singer sewing machine proven to contain red mercury.Mobile phones are supposedly employed as instruments to prove the existence of the phony substance. Popular belief in the Middle East has it that it can help uncover hidden gold treasures, though there are other theories which say it can be used to create a nuclear bomb."If the line cuts off when the telephone is placed close to the needle ... that proves the existence of the substance," Saudi Gazette said.Al-Eqtisadiah newspaper said "poverty provided a fertile ground for the red mercury rumor to spread in Saudi society, especially the middle class.""We have to find out who started this hoax. We cannot be 100 percent sure of getting in the short-term to the person or persons who started this," an interior ministry spokesman told Reuters."People hope to make profit. This is no different to cases of citizens who put their money in untrustworthy schemes," he added.Thousands of Saudi citizens have lost their life savings to financial scams consisting mainly of operations to raise money for real estate projects.Editing by Thomas Atkins and Paul Casciato