According to this Guardian article by Duncan Cambell (How the plotters slipped US net): “FBI assistant director Ron Dick, head of the
US National Infrastructure Protection Centre, told reporters that the
hijackers had used the net, and ‘used it well’.” (Sure, I get it….The same way that a gang of bank robbers “uses the roads, and uses them well” when they drive off in a getaway car…)

More from the story:

NSA has been attempting to keep up with the internet by building
huge online storage systems to hold and sift email. The first such
system, designed in 1996 and delivered last year, is known as
Sombrero VI. It holds a petabyte of information. A petabyte is a
million gigabytes, and is roughly equivalent to eight times the
information in the Library of Congress. NSA is now implementing a
Petaplex system, at least 20 times larger. It is designed to hold
internet records for up to 90 days.

Dr Gladman and other experts believe that, unless primed by
intelligence from traditional agents, these massive spy libraries are
doomed to fail. The problem with NSA’s purely technological
approach is that it cannot know what it is looking for. While
computers can search for patterns, the problem of correlating
different pieces of information rises exponentially as ever more
communications are intercepted. In short, NSA’s mighty
technology apparatus can easily be rendered blind, as happened
here, if it has nothing to start from.

The new legal plans may therefore do more harm than good.
According to Cambridge computer security specialist Dr Ian Miller,
bringing back escrow “will damage our security in other ways, and
divert an enormous amount of effort that would far better be spent
elsewhere. It won’t inconvenience competent terrorists in the least.

PGP inventor Phil Zimmermann thinks the penalty of politicians
misunderstanding technology will be even more costly. “If we install
blanket surveillance systems, it will mean the terrorists have won.
The terrorists will have cost us our freedom.”