Files seized in raid that killed Bin Laden reveal his role in planning potential terror attacks, including one on US rail system

Osama bin Laden stayed in touch with his al-Qaida network from his Pakistan safe house and continued to plot potential terrorist attacks, including one against the US railway system, according to early analysis of files seized when he was killed.

The special forces team who shot Bin Laden in the early hours of Monday took away a mass of digital information on computers, hard drives and storage discs, as well as paper documents. An initial trawl through the files indicate Bin Laden was not a mere figurehead for the militant group but remained closely involved in nuts-and-bolts planning, according to various US reports.

As late as February last year he seemingly took part in drawing up a previously unknown plot to attack a US commuter rail network, possibly on the 10th anniversary of the 9/11 attacks or another landmark date such as Christmas or new year, intelligence officials told US newspapers.

While the plot, apparently involving an attempt to derail a train by tampering with tracks, appeared to be only speculative, the seized documents seem to show Bin Laden was in regular contact with al-Qaida operatives from his house close to Pakistan's capital, Islamabad. Before the raid some analysts speculated that he had become an increasingly marginalised figure during his long presumed exile in remote tribal regions along the Afghan border.

Details have also emerged about the painstaking surveillance operation which preceded the raid on Bin Laden's hideout in Abbottabad, in which a CIA team spied on the house for months from a property they rented nearby. The officers scanned the compound using telephoto lenses and infrared imaging equipment, and attempted to listen in on conversations inside, anonymous US officials told the New York Times.

The surveillance team regularly spotted a tall man walking through the compound's courtyard, although they never confirmed whether this was Bin Laden.

Such was the cost of the operation that the CIA requested tens of millions of dollars in extra funding from Congress in December last year, officials told the Washington Post.

Staff at an FBI lab at the marine corps base in Quantico, Virginia, have been poring over the trove of data as quickly as possible in case they describe any imminent attacks, but as yet there have been no specific alerts.

"He [Bin Laden] wasn't just a figurehead," one unnamed US official told the New York Times. "He continued to plot and plan, to come up with ideas about targets and to communicate those ideas to other senior al-Qaida leaders."

The department of homeland security has ordered additional security at airports and other transport hubs, and issued a precautionary note about the railway plot. "As of February 2010, al-Qaida was allegedly contemplating conducting an operation against trains at an unspecified location in the United States on the 10th anniversary of 11 September 2001," it said. "As one option, al-Qaida was looking into trying to tip a train by tampering with the rails so that the train would fall off the track at either a valley or a bridge."

A department spokesman told the Washington Post that the plot appeared speculative: "We have no information of any imminent terrorist threat to the US rail sector."

The documents might prove more fruitful in leading the US to other senior al-Qaida figures, including Ayman al-Zawariri, al-Qaida's deputy leader. "We have lots of information on him," Mike Rogers, the Republican congressman who chairs the House intelligence committee, told the Washington Post. "I can't say it's imminent, but I do believe we're hot on the trail."

A day after laying a wreath to the victims of 11 September during a largely subdued visit to New York, Barack Obama is to travel to Fort Campbell, Kentucky, to meet the US Navy Seals who raided Bin Laden's compound.

Further reports have emerged confirming that the gun battle to secure the compound and kill Bin Laden was considerably more one-sided than initially presented by US officials.

"We expected a great deal of resistance and were met with a great deal of resistance," the White House spokesman, Jay Carney, said on Tuesday, adding that there were "many other people who were armed" beyond Bin Laden.

Now, further anonymous briefings to the US media have confirmed that only one of the five people killed in the operation was armed, and that the shots he fired came very early in the operation.

According to NBC News, the fighting was relatively brief and the Seals spent most of their time in the compound gathering computers and other data sources.