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“If we had the opportunity to take him alive, we would have done that,” he said. A U.S. official later told Reuters News Agency that the woman killed during the U.S. raid was not bin Laden’s wife and was not used as a human shield, but Mr. Brennan had not backtracked on his description of the events as of last night.

Lawmakers at the Capitol said the first inklings of intelligence that eventually led to bin Laden were collected years ago and that the operation serves notice that attacks against the U.S. and its allies will be punished.

“Justice has a long memory and has a long arm,” said Senate Armed Services Committee Chairman Carl Levin, Michigan Democrat.

Officials warned of the possibility of a retaliatory terrorist strike. Homeland Security Secretary Janet A. Napolitano said the U.S. is on heightened alert, but there is no specific or credible information to make her raise the terrorism-threat level.

Attention has turned to likely candidates to succeed bin Laden at the head of al Qaeda, and to how his death will affect the war on terrorism.

Senate Majority Leader Harry Reid, Nevada Democrat, said Mr. Obama told him that the withdrawal timetable for U.S. troops in Afghanistan will not change.

“The president has a timetable to begin withdrawal of Afghanistan,” Mr. Reid told reporters. “He’s indicated he’s going to stick with that. I think that’s appropriate.”

But Matthew Hoh, a senior fellow at the Center for International Policy and the director of the Afghanistan Study Group, said removing bin Laden should be a clear signal that it’s time to expedite the withdrawal.

“Where do we find bin Laden?” he asked. “In a villa, next to a Pakistani military academy an hour or two northeast of Islamabad. Families that have lost service members in Afghanistan are told their child or husband or wife is fighting al Qaeda and keeping us safe from terrorism. It has nothing to do with that. This needs to be a wake-up call.”

Mr. Hoh is a former captain in the Marine Corps who in 2009 resigned in protest of U.S. policy while serving with the State Department in Afghanistan.

U.S. officials are trying to determine what kind of support system bin Laden had in Pakistan and whether any members of the troubled country’s government were complicit in keeping his whereabouts under wraps, Mr. Brennan said. He refused to speculate, but noted it’s suspicious that bin Laden was found in Abbottabad, outside the major city of Islamabad.

“I think people are raising a number of questions and understandably so,” he said. “I’m sure a number of people have questions about whether or not there was some type of support that was provided by the Pakistani government.”

Some members of Congress are calling for more strings to be attached to military and civilian aid the U.S. funnels to Pakistan.