... U.S. intelligence got its first inkling of the plot from the contents of a laptop computer belonging to a Bahraini jihadist captured in Saudi Arabia early in 2003. It contained plans for a gas-dispersal system dubbed "the mubtakkar" (Arabic for inventive). Fearing that al-Qaeda's engineers had achieved the holy grail of terror R&D — a device to effectively distribute hydrogen-cyanide gas, which is deadly when inhaled — the CIA immediately set about building a prototype based on the captured design, which comprised two separate chambers for sodium cyanide and a stable source of hydrogen, such as hydrochloric acid. A seal between the two could be broken by a remote trigger, producing the gas for dispersal. The prototype confirmed their worst fears: "In the world of terrorist weaponry," writes Suskind, "this was the equivalent of splitting the atom. Obtain a few widely available chemicals, and you could construct it with a trip to Home Depot – and then kill everyone in the store." Having discovered the device, exposing the plot in which it might be used became a matter of extreme urgency. Although the Saudis were cooperating more than ever before in efforts to track down al-Qaeda operatives in the kingdom, the interrogations of suspects connected with the Bahraini on whose computer the Mubtakkar was discovered were going nowhere. The U.S. would have to look elsewhere.
Conventional wisdom has long held that the U.S. has no human intelligence assets inside al Qaeda. "That is not true," writes Suskind. Over the previous six months, U.S. agents had been receiving accurate tips from a man the writer identifies simply as "Ali," a management-level al-Qaeda operative who believed his leaders had erred in attacking the U.S. directly.... And when asked about the Mubtakkar and the names of the men arrested in Saudi Arabia, Ali was aware of the plot. He identified the key man as Bin Laden's top operative on the Arabian Peninsula, Yusuf al Ayeri, a.k.a. "Swift Sword," who had been released days earlier by Saudi authorities, unaware that al-Ayeri was bin Laden's point man in the kingdom...