Based on the information available, the Department of Homeland Security issued an intelligence message about potential al-Qaeda contemplation in February 2010 of plots against the US rail sector.
However, it said as of now it has no information of any imminent terrorist threat to the US rail sector, but wanted to make agencies aware of the alleged plotting; it is unclear if any further planning has been conducted since February of last year.
The New York Times reported that the documents include a handwritten notebook from February 2010 that discusses tampering with tracks to derail a train on a bridge, possibly on Christmas, New Year's Day, the day of the state of the Union address or the 10th anniversary of the September 11, 2001, attacks, officials said.
"We want to stress that this alleged al-Qaeda plotting is based on initial reporting, which is often misleading or inaccurate and subject to change," Department of Homeland Security spokesman Matt Chandler said in a statement.
"We remain at a heightened state of vigilance, but do not intend to issue an NTAS alert at this time. We will issue alerts only when we have specific or credible information to convey to the American public," Chandler said.
"Our security posture, which always includes a number of measures both seen and unseen, will continue to respond appropriately to protect the American people from an evolving threat picture both in the coming days and beyond," he said.
The department said that since bin Laden's killing, it has taken a number of actions, including critical infrastructure and transportation systems across the country, deploying additional officers to non-secured areas at nation's airports and identifying any new targeting rules that should be instituted to strengthen the ways they assess the risk of both passengers and cargo coming to the United States.
"It is not surprising that we would find this kind of information in the home of the world's most wanted terrorist," one US official quoted as saying by the CNN.
Material gathered from the same compound also suggests that al-Qaeda was particularly interested in striking Washington, New York, Los Angeles and Chicago, according to the official, the news channel said.
During the daring raid on May 2, US commandos found 10 hard drives, five computers and more than 100 storage devices, such as disks and thumb drives.
Commandos also recovered five cell phones, paper documents and five guns, including AK-47s and pistols.