How Much Risk Will We Take?

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Then why does the system remain so vulnerable to that brand of attack? The explosives-detection machines in airports today are not able to sniff out liquid explosives in a sealed container. Airline-security experts interviewed by TIME were divided on the question of whether the technology even exists to effectively detect liquid explosives in airports. Private companies have been working on various devices for years, but it's not clear if any are sufficiently accurate, cheap and fast. The fix is elusive because explosives can literally appear in any form--from computer paper to Jell-O, solid to gas--and they can be detonated by an endless mosaic of everyday devices. "Unless you are prepared to conduct intimate body searches or scans of every single passenger on every single flight, you cannot guarantee security from smuggled explosives. It's as simple as that," says Charles Shoebridge, a British security analyst and former counterterrorism officer.

Still, some experts believe the U.S. should be doing more to defend against bombs in general. The White House's Homeland Security Advisory Council has a director for nuclear threats and one for biochemical threats but no one specifically tasked to handle explosives. As in other parts of DHS, some of the best minds in the explosives unit have left in frustration. "There has been a hemorrhaging of talent," says a former senior U.S. official.

DHS has spent $732 million this year on aviation R&D for explosives-detection programs. Jackson said he did not have figures on hand for how much went to detecting liquid explosives in particular. Far more is spent on homeland security now compared with before 9/11, but many security experts say it's still not nearly enough. "The Pentagon's budget is 10 times that of DHS," notes Clark Kent Erwin, a former inspector general for DHS.

But given the hard reality of limited resources, what is the rational thing to do next? "Some people say, Let's push all the money into something that happened last week," says Chertoff. "[But] we still have to think about all the other things that could happen." Shoulder-fired missiles, for example, could be just as dangerous to plane passengers as liquid explosives. Some politicians argue that we should develop Star Wars-- style missile-defense technology to protect planes. But that would cost an estimated $10 billion to build and billions more to maintain.

It's worth considering the probability of an attack, not just the possibility. Once terrorists decide to bomb an airline with liquid explosives, how likely is it that they will succeed? Some 2,000 bombs are planted every year on U.S. soil, and almost none are liquid explosives. That's because they are extremely volatile. Some explode if dropped a couple of feet. Friction can set off TATP. It would be difficult, if not impossible, to check such a bomb in a suitcase. Even if the components are carried on separately--the safest strategy to avoid detection and premature detonation--mixing the materials produces a foul stench that would probably attract attention, according to a U.S. airline explosives expert.