One reason the terrorists who struck Sept. 11 eluded detection by America's vast intelligence network was their studied blandness.
They were, it seems, just too ordinary for anyone to notice.
Everything from their khaki-pants and polo-shirts attire to their use of mostly unencrypted e-mails and unsecure phones apparently enabled them to communicate freely with one another in planning the attacks, without ever attracting undue attention from US officials.
Thus, they exposed the soft underbelly of the nation's intelligence system: While its global eavesdropping network may be plenty powerful - intercepting daily millions of e-mail, cellphone, satellite phone, money transfer, and other communications - much of the data go unexamined. By some estimates, just 10 percent of the information plucked out is actually analyzed.
Since the attacks, critics have called for gathering more and better information through cloak-and-dagger "human intelligence." But close observers say perhaps the real lesson of Sept. 11 is the need to better synthesize data already being collected. Now there's new emphasis on hiring analysts, beefing up computers' "fuzzy logic" capabilities, and expanding the agencies' linguistic firepower.
Trying to glean specifics from the reams of data "is like holding a firehose to your mouth and trying to drink," says Loch Johnson, author of "Bombs, Bugs, Drugs, and Thugs: Intelligence and America's Quest for Security."
"There's a serious information-processing problem here," he says, recalling a director of the secretive National Security Agency telling him, "I have three problems: processing, processing, processing."
One signal that intelligence agencies had information about the attacks - but simply hadn't culled it out of their bulging databases - is that relatively quickly after Sept. 11, authorities identified and arrested many suspects. Immediately after the attacks happened, the clues made sense. But beforehand, they were unrecognizable amid a deluge of data.
"In hindsight, it's all there," notes Bruce Schneier, chief technology officer of Counterpane Internet Security in Cupertino, Calif. But in the fight against terrorism, "we need it to be there beforehand."
That's been true before. In 1995, for instance, a Chinese defector reportedly gave the Central Intelligence Agency some 13,000 documents that pointed to the theft of US nuclear secrets. But the CIA didn't fully translate those documents until four years later - after allegations became public that secrets had been stolen from the top-secret Los Alamos lab.
Indeed, across history, "intelligence agencies have been extraordinarily good at defining the threat ... and the capacity of that threat," says former Sen. Warren Rudman (R) of New Hampshire, co-chairman of the US Commission on National Security. "What they've been absolutely terrible at is predicting with any kind of certainty what those threats will do - and when they will do it."
He observes that the US had fairly good intelligence that the Japanese were willing and able to attack Pearl Harbor in 1941 - and that the Germans were preparing for the Battle of the Bulge in 1944. But intelligence agents weren't able to warn officials before the attack.
In modern America, that task has been made harder - and more expected - than ever.
The US has spent billions building a listening network unparalleled in history, codenamed Echelon. Its vast array of satellites and listening stations - supplemented by the so-called UKUSA alliance, which includes Great Britain, Australia, and New Zealand - enables it to listen to virtually any communication on earth.
But the task is made tougher by the massive flows of information. In 2000, Americans logged 2.58 billion minutes of cellphone use, up 75 percent from 1999.
E-mail use has exploded, too. America Online - the nation's biggest e-mail enabler - handles some 225 million e-mails and 1.1 billion instant messages a day.
The need to better analyze all this traffic has placed a renewed concentration on things like "fuzzy logic" computing. Rather than searching through transcripts of phone conversations for words like "bomb" or "hijack," new software can look for patterns of words that hint at terrorist action.
But observers say even the savviest computers won't be sufficient. Before the attacks, the CIA and other agencies were in the midst of a major recruitment drive. Now the need for analysts - especially those who speak Arabic or other Middle Eastern languages - is intense.
In the end, "the key in intelligence is always getting the right information to the right person at the right time," says former Rep. Lee Hamilton, who chaired the Intelligence Committee. Otherwise, he says, "You can have a warehouse of information, and it doesn't do you any good."