WASHINGTON - 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 in a firefight with US 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, singing "The Star-Spangled Banner" and "We Are the Champions," NBC News reported. Hundreds more sang and 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. Bin Laden, 54, was killed after a firefight with Navy SEALs and CIA paramilitary forces at a compound in the city of Abbottabad. He was shot in the head, NBC News reported. A US official told NBC News that bin Laden was later buried at sea "in accordance with Islamic law and tradition." Other US officials said one of bin Laden's sons and two of his most trusted couriers also were killed, as was an unidentified woman who was used as a human shield. Al Arabiya reported that two of bin Laden's wives and four of his children were also captured during the operation. Bin Laden was holed up in a two-story house 100 yards from a Pakistani military academy when four helicopters carrying four US forces swooped in, leaving his final hiding place in flames, Pakistani officials and a witness said.