The environment in Washington was further charged by a barrage of partisan attacks revolving around whether Mr. Obama bears ultimate responsibility for the security lapse, including a statement by former Vice President Dick Cheney that Mr. Obama “pretends” that the United States is not at war against terrorists.

A White House official fired back, blaming the Bush administration as having allowed Al Qaeda to thrive while it focused on the Iraq war.

A White House review into the episode is finding that agencies were looking at information without adequately checking other available databases  not because they were reluctant to share, as was the case before Sept. 11, but out of oversight or human error, said a senior administration official familiar with the review.

In interviews Wednesday, government officials and others provided an account of how various agencies had gleaned bits and pieces of information about the young Nigerian, but failed to pull them together to disrupt his plot. Most of the officials spoke only on the condition that they not be quoted by name.

The first sign of a threat came in August, when the National Security Agency, responsible for electronic eavesdropping around the world, intercepted the Qaeda conversations about the mysterious, unidentified Nigerian. That same month, Mr. Abdulmutallab arrived in Yemen and apparently soon began preparing for the Christmas Day attack.

Three months later, in November, Mr. Abdulmutallab’s father, a former senior Nigerian government official and a prominent banker, became panicked about his son’s turn to radicalism, according to an interview with a family cousin. The father beseeched Nigerian and American officials to intervene before his son did harm, said the cousin, who declined to be identified by name, citing the family’s desire for privacy.

The cousin, who attended a gathering of the family on Sunday, said that what alarmed Mr. Mutallab were the text messages his son had sent from Yemen. He said the son told the father that “he had found a new religion, the real Islam.” The son also texted that his family “should just forget about him; he’s never coming back,” the cousin recounted.