Al Qaeda cell had planned a 2003 cyanide attack on the New York subway system

U.S. authorities had intelligence that a team of Al Qaeda-linked terrorists had infiltrated the United States and planned a 2003 attack on the New York City subway system with homemade cyanide bombs, federal and local counterterrorism officials have acknowledged to NEWSWEEK. But the officials say the plot was called off at the last minute by Al Qaeda�s Ayman al-Zawahiri�for reasons that remain unclear.

Details of the purported cyanide plot are revealed by author Ron Suskind in his book, �The One Percent Doctrine,� to be published on June 20. According to a source familiar with the book�s content, Suskind reports that American authorities first learned about the cyanide plot from an informant inside Al Qaeda known as Ali. According to the book, Ali fed Washington critical information about Al Qaeda between late 2002 and early 2005, until U.S. officials decided that it was too dangerous to the informant to continue to use his reporting.

Suskind reports that in the spring of 2003, officials learned, apparently via Ali, that the Al Qaeda team was 45 days away from launching the subway attack. A few weeks earlier, U.S. intelligence had discovered that Al Qaeda had invented an improvised cyanide delivery system that the terrorists had dubbed mubtakkar, which Suskind says is an Arabic word for �inventive.�

The attack was never launched, Suskind reports, because Zawahiri, the principal deputy to Osama bin Laden, decided to call it off. Zawahiri remains at large and is believed to be with bin Laden. Suskind�s book claims that the terror cell responsible for the aborted attack remains at large inside the United States.

One former and two current U.S. counterterrorism officials (who all spoke to NEWSWEEK on condition of anonymity because of the sensitivity of the subject) confirmed the existence of intelligence information about the alleged cyanide plot and the existence of mubtakkar, the makeshift cyanide bomb. Two of the officials said that the device was actually quite primitive�put together with beer cans and soda bottles. Still, the officials say, models of the device built from Al Qaeda designs by U.S. authorities appeared to work.

The weapon was not regarded as the type of device that could cause large-scale, 9/11-style carnage, the officials said, but if set off in a crowded theater or arena was capable of killing hundreds of people.

The counterterrorism officials also confirmed Suskind�s reporting that U.S. intelligence indicated that the subway attack was called off personally by Zawahiri. Though the officials said U.S. intelligence was still not certain why the attack had been cancelled, one former official said some feared that Zawahiri had cancelled the subway attack because Al Qaeda was planning something even more deadly and spectacular inside the United States�an event that, if planned, so far has not materialized.