New York:
Sewn into the underwear of Umar Farouk Abdulmutallab was a powerful plastic explosive, the authorities say.
Had Abdulmutallab, sitting in seat 19A of Northwest Airlines Flight 253 on Friday from Amsterdam to Detroit, been able to set off the explosive, it might have blown a hole in the side of the airplane and caused it to crash, experts believe.
Abdulmutallab, 23, a Nigerian citizen, was charged in a federal criminal complaint on Saturday with the willful attempt to destroy an aircraft with an explosive device.
The complaint identified the explosive as pentaerythritol tetranitrate, or PETN.
Introduced after World War I, PETN is in the same chemical family as nitroglycerin and among the most powerful of explosives. It was the same explosive that Richard C. Reid tried to detonate in his shoes during an American Airlines flight in December 2001.
But one characteristic of PETN is that it does not easily detonate, and that apparently thwarted Abdulmutallab, officials said. Dropping it or setting it on fire will not typically detonate it, explosive experts said.
Usually, a shock wave from a blasting cap or an exploding wire detonator is needed to set off PETN. Abdulmutallab was reported to have used a syringe to try to inject a liquid into the explosive.
"It sounds like he was trying to cause a chemical reaction that would initiate it, and that didn't work out so well," said Jimmie C. Oxley, an explosives expert and professor of chemistry at the University of Rhode Island.
Some passengers aboard Flight 253 said they heard popping noises similar to firecrackers, smelled a burning odor and observed Abdulmutallab's pants leg and a wall of the airplane on fire. Passengers and crew members subdued Abdulmutallab and used blankets and fire extinguishers to put out the flames, according to the criminal complaint.
"A passenger stated that he observed Abdulmutallab holding what appeared to be a partially melted syringe, which was smoking," the complaint said. "The passenger took the syringe from Abdulmutallab, shook it to stop it from smoking and threw it to the floor of the aircraft."
FBI agents recovered what appeared to be the remnants of a syringe from near Abdulmutallab's seat, officials said, but the agency has not said what it suspects was in the syringe.
Oxley said it was conceivable that the contents of the syringe were sufficient to set off the PETN. "I've been thinking about it," she said. "I know what I would do now, but I'm not going to tell you."
In Reid's shoe bombs, in 2001, a highly unstable explosive known as triacetone triperoxide, or TATP, was the detonator for the PETN, but Reid failed to set it off when he was unable to light the fuse. But TATP is a solid, so it is unlikely that that was the substance in Abdulmutallab's syringe, Oxley said.