Intelligence about Mohammed's activities led in part to the orange alert that lasted most of February, said these officials, speaking on condition of anonymity.
"Some of the concerns we had that caused us to raise the threat level were attributable to the planning he was involved in," Homeland Security Secretary Tom Ridge told reporters Monday. "There were multiple reasons that we raised the threat level and his relation to one of the plot lines was one of the several."
Authorities recovered a huge amount of information about al-Qaida at the house in Pakistan where Mohammed and two others were arrested early Saturday, a senior law enforcement official said Monday.
This includes computers, disks, cell phones and documents that authorities believe will provide names, locations and potential terrorist plots of al-Qaida cells in the United States and around the world. Mohammed also was believed by U.S. officials to have details about the group's finances.
FBI and CIA officials were described as working around the clock to pore over the seized information to prevent any imminent attacks and to determine when and if more arrests could be made.
There was also the fear that even as officials work feverishly on the case, some of the al-Qaida operatives might go into hiding or halt any terrorist plots. It could also have the opposite effect of pushing al-Qaida cells to accelerate plots in the United States and elsewhere rather than run the risk of being captured.
Mohammed's interrogators - whether from the CIA, FBI or from a foreign security service - are working against the clock. His information about impending terrorist operations and the location of al-Qaida leaders and cells grows more dated by the hour.
Whether the CIA can learn anything useful from the alleged Sept. 11 mastermind depends on the skills and methods of the interrogators, Mohammed's willingness to talk and perhaps simply time.
Of top priority during the questioning is gaining intelligence that could help quickly disrupt attacks being planned or lead to added precautions, American counterterrorism officials said.
That could mean a domestic law enforcement raid to break up a cell ready to strike, or an increase of security at areas Mohammed names as targets subject to imminent attacks.
Overseas, it could mean an operation that leads to the capture of al-Qaida leader Osama bin Laden.
But such information is just what he is most likely to try to keep secret, or lie about. Still, terrorists who learn of Mohammed's capture may alter their plans, abandon safe houses or make hurried telephone calls - actions that could expose them to detection.
A U.S. intelligence memo dated Feb. 26 warned Mohammed was overseeing plans to have al-Qaida operatives in the United States attack suspension bridges, gas stations and power plants in New York and other major cities, Newsweek reported Sunday.
The only al-Qaida capture that approaches the magnitude of Mohammed's was that of Abu Zubaydah last March. Zubaydah more than once provided information that sent American security officials scurrying to provide warnings to cities and sectors of the economy, knowing all the while that he could be lying.
Officials were not releasing details of Mohammed's detention. Previous high-level al-Qaida captives have not been brought to U.S. soil; they would have rights not afforded on foreign soil, U.S. officials say. Where they are, however, has not been disclosed.
Another secret is how officials will attempt to get information from Mohammed. U.S. officials insist they eschew physical, violent torture, although it is unclear if all of America's allies live by a similar code.
Officials believe Mohammed can detail how Sept. 11 was put together, answering long-standing questions about the plot's origins: Who chose the World Trade Center and Pentagon as targets? Who picked Sept. 11 as the date?
American officials say Mohammed, who was born in Kuwait and has both Pakistani citizenship and ancestry, planned and coordinated key aspects of the Sept. 11 operation.
His information can be cross-checked with Ramzi Binalshibh's, his former aide who was captured in September. Binalshibh was a part of the cell that included Mohamed Atta, chief among the Sept. 11 hijackers.
In the mid-1990s, Mohammed also worked with his nephew Ramzi Yousef and two others in the Philippines on a number of operations. Yousef is in prison for his role in the 1993 World Trade Center bombing.
One plan called for bombing up a dozen trans-Pacific airliners in flight. A second involved crashing an airplane into CIA headquarters outside of Washington. Officials have suggested these plots - broken up in their infancy with the arrests of Mohammed's associations - were the seeds of Sept. 11.
The four plotters were linked to al-Qaida through a financial operative named Khalifa, who is bin Laden's brother-in-law, officials have said. Khalifa is believed to remain at large.