WEST PALM BEACH, Fla. – A U.S. senator revealed Tuesday that he believes a former FBI agent who disappeared in Iran nearly two years ago is being held in a secret prison there. Sen. Bill Nelson shed new light on the disappearance of Robert Levinson during a confirmation hearing for Hillary Rodham Clinton in Washington. Levinson, of Coral Springs, Fla., was last seen on Iran's Kish island in March 2007 where he had gone to seek information for a client of his security firm.