In this Sept. 11, 2001 file photo, the south tower begins to collapse as smoke billows from both towers of the World Trade Center, in New York. Osama bin Laden, the glowering mastermind behind the Sept. 11, 2001, terror attacks that killed thousands of Americans, was slain in his luxury hideout in Pakistan early Monday, May 2, 2011 in a firefight with U.S. forces, ending a manhunt that spanned a frustrating decade. (AP Photo/Jim Collins, File)