How Much Risk Will We Take?

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For many counterterrorism officials, the scale and depravity of the plot seem chilling enough to justify the drama. "Very seldom do things get to me," Chertoff told Congressman Peter King, chair of the House Homeland Security Committee, in a phone call late Wednesday night. "This one has really gotten to me." A British official says investigators believe the bombers planned waves of attacks. By blowing up planes over the Atlantic, they would make it nearly impossible to gather forensic evidence. Then after people returned to flying, the terrorists would strike again. That benign items--iPods and soda bottles, the stuff of teenagers' backpacks--could be turned into weapons of mass destruction seemed like a new, unsettling perversion. Or at least it felt new.

Despite the news-channel talk of a fresh threat, people have been trying for almost 20 years to blow up planes with liquid explosives packed in carry-on baggage. Terrorists, like movie studios and toddlers, don't like to try new things. In 1987 two North Korean agents posing as father and daughter put a radio packed with plastic explosives and a whisky bottle full of liquid explosives in a bag in the overhead bin of a South Korean airliner. Then they got off on a layover. The subsequent explosion sent the plane spinning into the jungle near the Thailand-Burma border, killing all 115 people onboard.

In 1994 al-Qaeda foreshadowed the London plot almost exactly when Pakistani terrorist Ramzi Yousef and Khalid Sheikh Mohammed, who went on to mastermind the 9/11 attacks, drew up a scheme to bomb 12 planes over the Pacific during a 48-hour period. They nicknamed the plan Bojinka. They intended to have five terrorists take liquid explosives in carry-on bags onto planes and then assemble the bombs onboard. All but one of the planes were to be U.S. bound. On Dec. 11, Yousef ran a dress rehearsal on a Philippine Airlines jet. He carried the explosives onboard in contact-lens-solution bottles. Like the North Koreans, he disembarked after positioning the bomb in the cabin. It successfully detonated, killing a Japanese passenger and injuring 10 others. But because of the very small quantity of explosives, it did not take down the plane. A month later, Yousef accidentally started a fire in his apartment while working with the explosives. The Bojinka plan was thwarted when police arrived to investigate and discovered a laptop containing details of the plot.

Since 1969, explosives have killed about 2,000 people on planes. "Explosive devices are--and will remain--the primary threat to aviation indefinitely," says Steve Luckey, a former security director of the Air Line Pilots Association. "Bomb components are easy to get, easy to hide, and the payoff is huge."

Liquid explosives are particularly diabolical. Like plastic explosives, a small amount of them can release a massive amount of force. And they can be easily disguised to look harmless. In 2002 the FBI issued a warning that al-Qaeda members had discussed sneaking onto planes liquid explosives disguised as coffee. The bombers who struck London's transit system in July 2005 used a variant of a peroxide-based explosive, triacetone triperoxide (TATP). "We didn't wake up and discover liquid explosives this week," says DHS Deputy Secretary Michael Jackson.