Osama bin Laden, the mastermind behind the Sept. 11, 2001, terror attacks that killed thousands of Americans, was slain in his luxury hideout in Pakistan early Monday in a firefight with U.S. forces, ending a manhunt that spanned a frustrating decade.

"Justice has been done," President Barack Obama declared as crowds formed outside the White House to celebrate. Many sang "The Star-Spangled Banner" and "We Are the Champions," NBC News reported.

Hundreds more waved American flags at ground zero in New York — where the twin towers that once stood as symbols of American economic power were brought down by bin Laden's hijackers 10 years ago.