Information obtained during the raid on Osama Bin Laden's compound indicates Al Qaeda was planning attacks in American cities on significant dates, according to a rail security alert issued Thursday.
The DHS notice is the first such notice that can be linked to the early Monday morning raid on the Abbottabad, Pakistan compound in which the Al Qaeda leader was found and assassinated.
The notice said in February 2010 Al Qaeda members discussed a plan to derail trains in the US by placing obstructions on the tracks.
The plan was to be executed on 11 September 2011 - the tenth anniversary of the 9/11 Al Qaeda attacks on the World Trade Center and Pentagon that claimed a total of 2,977 innocent lives.
"It's not surprising that we would find this kind of information in the home of the world's most wanted terrorist," one US official told CNN.
DHS confirmed the notice went out to federal, state, local and tribal authorities.
"This alleged Al Qaeda plotting is based on initial reporting, which is often misleading or inaccurate and subject to change," DHS spokesman Matt Chandler told reporters.
"We have no information of any imminent terrorist threat to the US rail sector," Chandler clarified. "But we wanted to make our partners aware of the alleged plotting; it is unclear if any further planning has been conducted since February of last year."
During the raid ten hard drives, five computers, and more than 100 storage devices, such as disks and thumb-drives, were seized a senior official told CNN. Five mobile phones, paper documents and five firearms, including AK-47's and pistols, were also recovered.
US intelligence officials said Al Qaeda appeared especially interested in striking on significant dates like July 4, Christmas and the opening day of the United Nations.
Al Qaeda was particularly interested in striking Washington, New York, Los Angeles, and Chicago, the officials said.
One US official speaking to CNN on condition of anonymity said, "valuable information has been gleaned already."