Al Qaeda suspect reveals communication strategy
New terror warning based on pre-9/11 surveillance
U.S. officials say al Qaeda info is dated but had been updated recently.
Pakistan, U.S. working closely in fight against terror.
Key institutions opened for business despite terror alert.
WASHINGTON (CNN) -- The man arrested in Pakistan with documents that sparked this week's increased threat levels is a computer expert who helped Osama bin Laden communicate with his terror network, U.S. government sources told CNN.
U.S. officials have identified the suspect as Muhammad Naeem Noor Khan, but Pakistani officials said the man's identity could not be confirmed because he has used multiple aliases in the past.
U.S. sources said Khan told interrogators al Qaeda uses Web sites and e-mail addresses in Turkey, Nigeria and tribal areas of Pakistan to pass messages among themselves.
Couriers were often used to deliver computer discs, and Khan would then post the messages on Web sites, but only briefly, the sources said.
According to the sources, after messages were sent and read, the files were deleted.
E-mail addresses were used only two or three times; if the information was really sensitive, an address might be used only once.
It was Khan's capture on July 13 that resulted in a wealth of information about al Qaeda and led to Sunday's raising of the terror threat level around key U.S. financial institutions in three cities.
The U.S. sources said Khan assisted in the evaluation of potential targets and served as a "clearing house" of information. He told investigators that he does not know where bin Laden is hiding, the sources said.
The sources said Khan's father facilitated a lot of his international travel, but they do not think the father knew what his son was up to.
Intel possibly updated recently
Much of the surveillance of possible terror targets in New York, Newark, New Jersey, and Washington, D.C., took place before September 11, 2001, but there was an indication of reconnaissance updates as recently as January, Bush administration officials said Tuesday.
"We know from the way al Qaeda does business, including on the 9/11 attacks, that they do their homework well in advance, then they update it just before they launch an attack," said Frances Fragos Townsend, a homeland security adviser to President Bush.
U.S. Homeland Security Secretary Tom Ridge said some of the information was updated earlier this year but that "there's no evidence of recent surveillance."
Neither Ridge nor Townsend said how much information was updated in January.
A senior military U.S. official said a computer seized from Khan contained hundreds of images, including photographs, drawings and layouts of various potential U.S. targets. (Full story)
Some of the photos were years old, while others had been taken as recently as the past few months, the official said. Some images showed underground garages, leading to the conclusion those areas had been under surveillance.
But the information did not include details of any specific plot or time.
"These reports are extraordinarily detailed," Townsend said. "These individuals clearly had access; they were inside this country, inside these targets, crawling all over them, making sure they understood those buildings."
Pakistani 'breakthrough' touted
Pakistani information minister Rashid Ahmad said that in addition to Khan, Pakistani security forces had captured "valuable people" who provided "valuable information."
"It is a great achievement of our security forces," Ahmad said. "It is a great breakthrough in the al Qaeda network."
Ahmad would not reveal any other information, saying it was "best not to say too much."
As Pakistani officials have in the past, he said more information might be forthcoming.
"We may be in the position to get some good fish in the coming days," he said.
Ahmed Khalfan Ghailani -- a Tanzanian arrested in Pakistan last week in connection with al Qaeda's bombings of U.S. embassies in East Africa in 1998 -- also provided "very important" information, Ahmad said Monday.
In addition, a senior Pakistani intelligence official said seven more suspected al Qaeda members have been taken into custody since Ghailani's arrest -- including one who was trying to leave the country Monday morning.
Ridge commends workers
In raising the alert level Sunday, Ridge said the intelligence suggested terrorists may be targeting the New York Stock Exchange and Citigroup headquarters in New York, insurance giant Prudential Financial's headquarters in Newark, New Jersey, and the International Monetary Fund and World Bank buildings in Washington. But he said nothing indicated that attacks were imminent. (Full story)
The color-coded alert level for terror threats in those three areas is now at orange, or high.
An NYPD officer stands guard outside the New York Stock Exchange.
The rest of the nation remains at threat level yellow, or elevated. Orange is the second-highest level, just above yellow and just below red, or severe.
Sunday's move was the first time the alert system had been applied to specific areas, though New York City has been on orange alert since the scheme was put in place after the terrorist attacks of September 11, 2001.
At a news conference Tuesday morning at the Citigroup financial building in Manhattan, Ridge commended employees for their conduct and decisions to work.
"The terrorists wish to make Americans that live in freedom, live in fear," Ridge said. "Just by showing up at work, you have made a powerful statement that they will not succeed."
New York Mayor Michael Bloomberg his city would not "be cowed by the terrorists."
In Washington, Metropolitan Police Chief Charles Ramsey and Capitol Hill Police Chief Terrance Gainer said they expected increased security around buildings to remain in effect through at least the November 2 election.
Government officials said the NASDAQ "market site" in Times Square and the American Stock Exchange in New York and the Bank of America building in San Francisco, California, also were mentioned in the recent intelligence.
CNN's Kelli Arena, Kevin Bohn, Syed Mohsin and Barbara Starr contributed to this report.