How a Detainee Became An Asset

Mohammed told interrogators that after the Sept. 11 attacks, his "overriding priority" was to strike the United States, but that he "realized that a follow-on attack would be difficult because of security measures." Most of the plots, as a result, were "opportunistic and limited," according to the summary.

One former agency official recalled that Mohammed was once asked to write a summary of his knowledge about al-Qaeda's efforts to obtain weapons of mass destruction. The terrorist group had explored buying either an intact nuclear weapon or key components such as enriched uranium, although there is no evidence of significant progress on that front.

"He wrote us an essay" on al-Qaeda's nuclear ambitions, the official said. "Not all of it was accurate, but it was quite extensive."

Mohammed was an unparalleled source in deciphering al-Qaeda's strategic doctrine, key operatives and likely targets, the summary said, including describing in "considerable detail the traits and profiles" that al-Qaeda sought in Western operatives and how the terrorist organization might conduct surveillance in the United States.

Mohammed was moved to the U.S. military facility at Guantanamo Bay, Cuba, in September 2006, and his loquaciousness is now largely confined to occasional appearances before a military commission. Back in his 86-square-foot cell at the secret Camp 7 at Guantanamo, he spends most of his waking hours in prayer, according to a source familiar with his confinement who spoke on the condition of anonymity.

But Mohammed has not abandoned his intellectual pursuits. He requested a Bible for study in his cell, according to the source, in order to better understand his enemy.

Staff writer Walter Pincus contributed to this report.