Ray Kelly: 'a dirty bomb' is the greatest threat facing the U.S.

Former NYPD commissioner Ray Kelly spoke to Yahoo News and Finance Anchor Bianna Golodryga about his memoir "Vigilance: My Life Serving America and Protecting Its Empire City." He reflected on the 15th anniversary of the Sept. 11 attacks and told Golodryga that the threat he fears the most is "a dirty bomb."