Congrats to the folks within the U.S. intelligence community. Turns out the cyber component of this arrest was the most significant.

The unannounced capture of a figure from Al Qaeda in Pakistan several weeks ago led the Central Intelligence Agency to the rich lode of information that prompted the terror alert on Sunday, according to senior American officials. The figure, Muhammad Naeem Noor Khan, was described by a Pakistani intelligence official as a 25-year-old computer engineer, arrested July 13, who had used and helped to operate a secret Qaeda communications system where information was transferred via coded messages.
A senior United States official would not confirm or deny that Mr. Khan had been the Qaeda figure whose capture led to the information. But the official said “documentary evidence” found after the capture had demonstrated in extraordinary detail that Qaeda members had for years conducted sophisticated and extensive reconnaissance of the financial institutions cited in the warnings on Sunday.
One senior American intelligence official said the information was more detailed and precise than any he had seen during his 24-year career in intelligence work. A second senior American official said it had provided a new window into the methods, content and distribution of Qaeda communications.
“This, for us, is a potential treasure trove,” said a third senior American official, an intelligence expert, at a briefing for reporters on Sunday afternoon.
The documentary evidence, whose contents were reported urgently to Washington on Friday afternoon, immediately elevated the significance of other intelligence information gathered in recent weeks that had already been regarded as highly troubling, senior American intelligence officials said. Much of that information had come from Qaeda detainees in Afghanistan and Saudi Arabia as well as Pakistan, and some had also pointed to a possible attack on financial institutions, senior American intelligence officials
said.
The American officials said the new evidence had been obtained only after the capture of the Qaeda figure. Among other things, they said, it demonstrated that Qaeda plotters had begun casing the buildings in New York, Newark and Washington even before the attacks of Sept. 11, 2001. Among the questions the plotters sought to answer, senior American intelligence officials said, were how best to gain access to the targeted buildings; how many people might be at the sites at different hours and on different days of the week; whether a hijacked oil tanker truck could serve as an effective weapon; and how large an explosive device might be required to bring the buildings down.