was among the people who were discussing the rail threat that prompted Thursday's notice from the Department of Homeland Security, a U.S. official said Friday.
The information was found in a paper document, not in a computer.
A law enforcement official said Thursday that, as early as February 2010, al Qaeda members discussed a plan to derail trains in the United States by placing obstructions on tracks over bridges and valleys.
The plan was to be executed later this year, coinciding with the 10th anniversary of the September 11 attacks, though no specific rail system was identified, the official said.
The Department of Homeland Security confirmed that a notice had been sent to federal, state, local and tribal authorities and a spokesman for Amtrak said its employees were on a heightened "state of vigilance."
In addition, videotapes found in bin Laden's compound are being "aggressively analyzed," the official said.
Speaking generally about the material that has been analyzed, the U.S. official said, "The information collected suggests that he (bin Laden) had not only a strategic role but also worked at the operational and even tactical levels. ... He was clearly issuing directions at all levels."
Rep. Mike Rogers, R-Michigan, told CNN Thursday that the United States is hot on the trail of Ayman al Zawahiri.
But the U.S. official would not characterize the state of the search for bin Laden's possible successor beyond calling it "relentless."
Thesuccession plan calls for Zawahiri to take over the top spot, but it is unclear if the organization's leaders will follow the plan, the U.S. official said, adding, "There are other players who could assume the leadership mantle."
Among those who could make a bid for assuming the leadership role is, the U.S.-born cleric who is a key figure in al Qaeda in the Arabian Peninsula.