Surveillance Net Yields Few Suspects

Until Bush secretly changed the rules, the government could not tap into access points on U.S. soil without a warrant to collect the "contents" of any communication "to or from a person in the United States." But the FISA law was silent on calls and e-mails that began and ended abroad.

Even for U.S. communications, the law was less than clear about whether the NSA could harvest information about that communication that was not part of its "contents."

"We debated a lot of issues involving the 'metadata,' " one government lawyer said. Valuable for analyzing calling patterns, the metadata for telephone calls identify their origin, destination, duration and time. E-mail headers carry much the same information, along with the numeric address of each network switch through which a message has passed.

Intelligence lawyers said FISA plainly requires a warrant if the government wants real-time access to that information for any one person at a time. But the FISA court, as some lawyers saw it, had no explicit jurisdiction over wholesale collection of records that do not include the content of communications. One high-ranking intelligence official who argued for a more cautious approach said he found himself pushed aside. Awkward silences began to intrude on meetings that discussed the evolving rules.

"I became aware at some point of things I was not being told about," the intelligence official said.

'Subtly Softer Trigger'

Hayden has described a "subtly softer trigger" for eavesdropping, based on a powerful "line of logic," but no Bush administration official has acknowledged explicitly that automated filters play a role in selecting American targets. But Sen. Arlen Specter (R-Pa.), who chairs the Judiciary Committee, referred in a recent letter to "mechanical surveillance" that is taking place before U.S. citizens and residents are "subject to human surveillance."

Machine selection would be simple if the typical U.S. eavesdropping subject took part in direct calls to or from the "phone numbers of known al Qaeda" terrorists, the only criterion Bush has mentioned.

That is unusual. The NSA more commonly looks for less-obvious clues in the "terabytes of speech, text, and image data" that its global operations collect each day, according to an unclassified report by the National Science Foundation soliciting research on behalf of U.S. intelligence.

NSA Inspector General Joel F. Brenner said in 2004 that the agency's intelligence officers have no choice but to rely on "electronic filtering, sorting and dissemination systems of amazing sophistication but that are imperfect."

One method in use, the NSF report said, is "link analysis." It takes an established starting point -- such as a terrorist just captured or killed -- and looks for associated people, places, things and events. Those links can be far more tenuous than they initially appear.

In an unclassified report for the Pentagon's since-abandoned Total Information Awareness program, consultant Mary DeRosa showed how "degrees of separation" among the Sept. 11 conspirators concealed the significance of clues that linked them.

Khalid Almihdhar, one of the hijackers, was on a government watch list for terrorists and thus a known suspect. Mohamed Atta, another hijacker, was linked to Almihdhar by one degree of separation because he used the same contact address when booking his flight. Wail M. Alshehri, another hijacker, was linked by two degrees of separation because he shared a telephone number with Atta. Satam M.A. Al Suqami, still another hijacker, shared a post office box with Alshehri and, therefore, had three degrees of separation from the original suspect.