Declaring the killing of Osama bin Laden "a good day for America," President Barack Obama said Monday the world was safer without the al-Qaida terrorist and mastermind of the Sept. 11, 2001 attacks. His administration used DNA testing to help confirm that American forces in Pakistan had in fact killed bin Laden, as U.S. officials sought to erase all doubt.

"Today we are reminded that as a nation there is nothing we can't do," Obama said. He hailed the pride of those who broke out in overnight celebrations as the stunning news spread around the globe.

An elite crews of American forces killed bin Laden during a daring raid on Monday. Bin Laden was shot in the head during a firefight and then quickly buried at sea. White House officials were mulling the merits and appropriateness of releasing a photo.

As spontaneous celebrations and expressions of relief gave way to questions about precisely what happened and what comes next, U.S. officials warned that the campaign against terrorism is not nearly over — and that the threat of retaliation was real.

Senior administration officials said the DNA testing alone offered near 100 percent certainty that bin Laden was in fact shot dead. Detailed photo analysis by the CIA, confirmation by a woman believed to be bin Laden's wife on site, and matching physical features like bin Laden's height all helped confirmed the identification.