Mr. Shahzad recounted how and why he conceived the plot, traveling to Pakistan last year, joining the Taliban and receiving training in how to construct a bomb.
The international hunt for those behind the plot is focusing on a Saudi-born extremist linked to al-Qaida in Yemen, who is also accused of constructing a bomb planted on a US plane on Christmas day.
The man, Ronald A. Grecula, 68, of Bangor, Pa., boasted to an undercover F.B.I. agent that he could use his background in engineering and welding to construct a bomb that would leave a crater 20 feet wide, according to a Justice Department filing.
American intelligence experts have said Al Qaeda, which enjoys the Taliban's protection in Afghanistan, had made repeated attempts over the years to acquire fissionable material to construct a bomb.
A 20-year-old Saudi student who was arrested in Lubbock, Tex., late Wednesday was close to constructing a bomb and had researched possible targets, including the Dallas home of former president George W. Bush and the residences of three Americans who served at the Abu Ghraib prison in Iraq, authorities said.
Despite Mr. Netanyahu's contention that Iran is close to developing a nuclear weapons capacity, administration officials have said there would still be time for the United States and others to detect and, if necessary, respond to an effort to move from merely enriching to constructing a bomb.
Yet was not, evidently, stopped from obtaining the know-how or materials to construct a bomb.
Will you continue to contain Iran and add pressure through sanctions until it is clear Iran is constructing a bomb?
Milligan subsequently reported that the book contained instructions on how to construct a bomb.
