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Information uncovered at Osama bin Laden's compound after his death shows al-Qaida considered attacking trains on the 10th anniversary of Sept. 11, officials said.
An advisory has been sent to law enforcement officials asking them to be vigilant about train security based on the new details. The FBI and the Department of Homeland Security are telling officials to watch for clips or spikes missing from train tracks, debris placed on tracks and frequent trespassing on railroad property.
Federal officials are also warning law enforcement to watch out for thefts of items like maintenance tools and identification badges, and for people without qualifications attempting to gain railroad employment.
"We continue to operate under the premise that terrorists not yet identified by the intelligence community and law enforcement may be operating in the United States and could advance and execute attacks without warning," an updated advisory said Friday.
The train warnings came as al-Qaida issued a statement Friday confirming bin Laden's death and pledging that "we will pursue the Americans and their agents both inside and outside their country, and soon, with the help of Allah."
There is nothing specific to New York in the train warning information or the latest al-Qaida statement. Some New Yorkers said Friday that the latest terror scares are worrisome, but nothing new.
Lucinda Hicks-Beach Quinn said she would remain vigilant.
"I'm slightly concerned, but not going to change anything I do," she wrote on NBC New York's Facebook page.
Daria D'Elia said "we Americans will not live in fear. If we do, they win! We will be more alert is all!"
Officials stress that the train advisories are general, and the information apparently uncovered from the bin Laden house in Pakistan dates back more than a year.
U.S. officials say they have not found reference to specific plots. Instead, they say they've found what they call "aspirational" items -- events al-Qaida operatives were interested in trying to make happen.
"We have no information of any imminent terrorist threat to the U.S. rail sector, but wanted to make our partners aware of the alleged plotting," Department of Homeland Security spokesman Matt Chandler said in a statement."We want to stress that this alleged al-Qaida plotting is based on initial reporting, which is often misleading or inaccurate and subject to change,"
A government advisory sent Thursday says that as far back as February 2010, al-Qaida was contemplating "an operation against trains at an unspecified location in the United States on the 10th anniversary" of the 9/11 attacks.
One option, the advisory says, was trying to tip a train by tampering with the rails so that the train would fall off the track at either a valley or on a bridge. Such an attempt would probably only work once, the material in bin Laden's house said, because tilting or tampering with the rails would be spotted, the advisory says.
Other material mentions a desire to target major mass-transit hubs.
One former official who worked directly on post-9/11 strategy called the stepped-up security in the aftermath of bin Laden's death a "race against time."
"If they were planning on doing something here in New York or another city, and they know that in fact we're going through the hard drives, taking the information and the data and we're starting to pull things together, they want to be able to maybe push up their event and try to have it take place before we get to them or before we're on to them and we prevent it from happening," said Robert Strang, formerly of the New York post-9/11 terror task force.
But at least one regular New Yorker said that if something's going to happen, it's going to happen.
"You can't build your days and yours lives around a fear of that," said the unidentified commuter.
The FBI and Homeland Security are encouraging local governments to be vigilant. But there are no plans to issue a terror alert, because there's still no specific or credible intelligence of any actual attack plan in the works.