Law enforcement officials were trying to determine whether the plot was current, with terrorists still trying to organize such an attack — in an investigation made more urgent by revelations linking the suspect behind the intelligence with the 1998 bombings of U.S. embassies in east Africa.
In those devastating truck bombings, al Qaeda operatives had begun casing targets in Kenya almost five years in advance.
The warnings that terrorists might be plotting attacks on specific buildings in New York, Washington and Newark, N.J., have prompted authorities to elevate the terror alert level for the financial sector in those cities to orange, or high. Streets have been closed, with barricades erected and heavily armed police guarding potential targets.
The intelligence behind the warnings — including hundreds of detailed surveillance photos, sketches and written documents — came from sources including a seized laptop and computer discs and from interviews after the mid-July arrest of a young Pakistani computer engineer, Mohammad Naeem Noor Khan.
Federal investigators are working on the assumption that the plot is continuing, said a senior Justice Department official, speaking on condition of anonymity. Two counterterrorism officials, also speaking anonymously, said information and evidence uncovered suggests that terrorists were recently using the information from surveillance activities.
And top Bush administration officials said pieces of the surveillance — including images — were apparently updated as recently as this January, although they offered no specific details.
Law enforcement agencies are searching for the al Qaeda operative who wrote the surveillance reports, and CBS News National Security Correspondent David Martin reports officials who have read the documents say the author was clearly and English speaker.
"I think you have to keep in mind al Qaeda's history of planning attacks well in advance and then updating those plans just before attacking," said White House spokesman Scott McClellan, traveling with President Bush on a trip to Texas.
Administration officials denied any suggestion that raising the terror alert right after the Democratic National Convention was politically motivated. "We don't do politics in the Department of Homeland Security," Ridge said.
He said it was essential to release the information, which had just been uncovered in Pakistan. Speaking at a news conference in New York, Ridge said that because of the heightened security steps, "we have made it much more difficult for the terrorists to achieve their broad objectives."
Democratic presidential candidate John Kerry, who received a special intelligence briefing on the terror threat Sunday, ducked the question when asked whether he, as president, would he have authorized his homeland security chief to issue the same warning as Ridge.
"Senator Kerry never comments directly or indirectly on the information he receives in intelligence briefings," spokeswoman Debra DeShong said Tuesday.
On Sunday, when the terror alert was issued — mentioning the Citigroup Center building and the New York Stock Exchange in New York, the International Monetary Fund and World Bank buildings in Washington and Prudential Financial Inc.'s headquarters in Newark, N.J. — officials acknowledged that some of the information was at least several years old, some of it preceding the Sept. 11, 2001, attacks.
In addition to the five buildings, one of the counterterrorism officials said the information included references to the Nasdaq and American Stock Exchange buildings in New York and the Bank of America building in San Francisco. Two other facilities in New York and undisclosed buildings in Washington and New Jersey were also mentioned.
But even with the extensive amounts of information, a full outline of a plot was not included, one official said. Instead, authorities are following leads. For instance, another official said surveillance reports were written in English, indicating the author spent significant time in the West.
And many of the paper documents showing the surveillance of U.S. buildings were undated, meaning investigators must work backward to match particular descriptions of security with known details of security at the buildings at certain points in time to determine when the documents were created.
One link under investigation is between Khan, the source of the surveillance documents, and the 1998 bombings in Kenya and Tanzania that killed more than 200 people, said the Justice Department official.
Shortly after Khan was captured, Pakistani police arrested, a Tanzanian sought by U.S. officials for the 1998 bombings in east Africa. There was a $25 million bounty for his capture.
Under questioning, Ghailani — who is cooperating with investigators — corroborated the material that was found in the surveillance documents, said the senior Justice Department official.
Ridge said there was no indication that terrorists had infiltrated the financial institutions themselves to obtain information about them. That view was echoed Tuesday by a World Bank spokesman, Damian Milverton.
"There is no suggestion that al Qaeda penetrated the building here at all," Milverton said.
But the Justice official said there are indications that the surveillance was detailed enough that people who work in the buildings might have knowingly or unknowingly assisted — perhaps by inadvertently giving out information.
The raising of the terror alert so far has not become a major issue in the presidential campaign.
But Larry Johnson, a former State Department deputy chief of counterterrorism, said the information about possible attacks is too vague to be useful and could lead to "warning fatigue."
"This is like the fifth time we've been warned that the end is imminent," he said. "Then it passes and nothing happens and what I fear is that people are going to become increasingly jaded about it."