Did al Qaeda plot to release cyanide gas in New York City subways? A new book details the alleged plan, but the former chief of White House counterterrorism said there are reasons to be skeptical about the report.
The terror network supposedly planned to release the deadly gas in subway cars in 2003, according to an upcoming book by Pulitzer Prize winner Ron Suskind.
In his new book, "The One Percent Doctrine: Deep Inside America's Pursuit of Its Enemies Since 9/11," Suskind wrote that an al Qaeda cell in the United States came within 45 days of attempting to detonate a crude device with small containers of deadly chemicals.
Since the 9/11 attacks, Islamic radicals have targeted trains in London and Madrid.
Clarke is wary of the report, however.
"There's reason to be skeptical," said ABC News consultant Richard Clarke, who is the former chief of White House counterterrorism. "Just because something is labeled in an intelligence report does not mean every word in it is true."
He said the information describing the plot would have been just one of the hundreds of threats that would have been collected in 2003.
Furthermore, the specificity of the report is suspect, he said.
"Whenever you get reports that are this specific, they are usually made up," he said.
Clarke noted the report detailed a particular time period for the attack, and that Osama bin Laden's top deputy himself weighed in.
Clarke said Ayman al-Zawahiri and bin Laden are too isolated to have that kind of direct control over a plot inside the United States. He also believes the terrorists would have carried out the attack if the plot was as advanced as Suskind reported.
"Frankly if there was a team in the United States that was ready to do this, they would have done it," Clarke said.
Regardless, an attack on mass transit could have a devastating effect.
A device packed with explosives and poison gas could kill hundreds if successfully detonated, experts said.
"Any of that stuff in a finite space is extremely dangerous," said Jack Cloonan, a former FBI counterterrorism agent. "If you want to do something terrible to New York City, you would come here when most people are here, rush hour in the morning or rush hour at night."
New York, Washington and other major cities have since installed sensors to detect poison gas.
In 1995, 12 people died after a deadly sarin gas attack on the Tokyo subway system.
"Attacks like this have been staged before with less successful results, perhaps, but the fact of the matter is this is exactly the kind of situation we should be looking for," said ABC News consultant Kyle Olson.
U.S. officials obtained the device's design from Islamic Wweb sites associated with al Qaeda.
Top al Qaeda officials discussed this plot in 2003, but there's no evidence a cell was in the United States ready to carry out the mission, according to law enforcement sources.
Suskind reported the attack was called off by Osama bin Laden's top lieutenant, Ayman al-Zawahiri.
In March 2003, the FBI warned, "Little or no training is required to assemble and deploy such a device due to its simplicity."
ABC News' Pierre Thomas contributed to this report.