As the 20th anniversary of the Sept. 11, 2001, attacks approaches, a new biography traces Osama bin Laden's path from a shy, religious teenager to the leader of a global jihadist group dedicated to mass murder. Journalist Peter Bergen, who met the al-Qaida leader in 1997, says that a series of events kept pushing bin Laden "further and further down the path of radicalization." Bergen's new book is 'The Rise and Fall of Osama bin Laden.'