supposed to detonate aboard the airplanes carrying them. The bombs, hidden in printer cartridges, were hooked up to cell phones without SIM cards, the New York Times reports today, so calling the phones during intercontinental travel couldn’t have set them off. And experts point out that calling a phone to activate a bomb aboard a plane is one of the least-efficient detonation methods that terrorists targeting aircraft can choose.

“They couldn’t call,” says Roger Cressey, a former counterterrorism official in the Clinton and George W. Bush administrations now with Goodharbor Consulting. If the terrorists used a regular cell phone to call an airplane-borne bomb from a great distance, it probably wouldn’t be able to reach a tower that could bounce a signal to the phone — though it’s not impossible. More likely, Cressey speculates, the bombmakers would have timed the phone’s alarm to go off, triggering the bomb. “If they set the alarm, say, two days in advance, and they had confidence how it was shipped and packed to the U.S., then they’d have confidence about where it would be when [it went] boom,” he says.

A Pentagon adviser who specializes in stopping improvised bombs — and who would only talk on condition of anonymity — cautions that a satellite phone would have the signal strength to reach the phone packed into the printer-bomb. But keeping that phone ready to receive calls “increases your risk of detection from the device, because you’re emitting a signal.” The adviser also said the bombmakers would rely on the phone’s alarm to trigger the explosion.

That still relies on two key assumptions. First, that the terrorists had reliable-enough information about the airborne methods of shipping used by FedEx and UPS, the two carriers chosen to unwittingly transit the bombs. (Presumably, they could track the movements of their parcels online.) And second, that the phones hooked up to the explosives in the printers housing the bombs would have enough battery life not to die out before any such alarm trilled.

It’s not yet clear why the bombs didn’t explode; an investigation of the printer-bomb plot is still ongoing. Brennan said on television yesterday that the “sophisticated” bombs were “able to be detonated at a time of the terrorists’ choosing.” But it’s easy enough in theory to control a bomb using a cellphone, as insurgents in Iraq demonstrated for years with their improvised explosive devices. Hook a battery charge up to a cellphone’s standard motor — which spins when someone calls or the alarm rings — and then rig the battery to an explosive substance. Instant bomb.

Despite that, it’s “pretty damn hard” to succeed at a mail-borne intercontinental bombing, says a former intelligence official who requested anonymity because he’s still a government employee: “You stick it in the mail, it goes on a plane, the plane’s gonna fly, but you better hope it goes off.”

U.S. officials have been cautious about attributing responsibility for the plot to al-Qaeda. But if al-Qaeda is the culprit, the Pentagon adviser says, the terror group is showing “declining capability.” Hijacking multiple aircraft on 9/11 is much more complex than trying — unsuccessfully — to blow up a pair of passenger or cargo planes.

Of course, it’s possible that the bombs had redundant triggering mechanisms in case of initial failure. In that case, the terrorists might have had provided the bombs’ cellphone number to U.S.-based operatives to call when the packages arrived. Even so, the phone would have to have sufficient power to set the explosion in motion — and the terrorists would have incurred the risk of emitting a signal from the bomb-phone. “In sleep mode, you’d have enough time, maybe 24-48 hours” to get the charge going, Cressey says. No wonder the terrorists apparently opted for the industry shipping leaders.

The logistical difficulties in setting off the bomb might strengthen the theory that the printer-bomb plot was a terrorist test run — a theory that took a hit now that ABC News reported there already was a probable test run for the bomb plot in September. Then again, the chief bombmaker for al-Qaeda in the Arabian Peninsula, Ibrahim Hassan al-Asiri, has failed to kill anyone in his two previous high-profile bombing attempts: the thwarted Christmas Day attack, which failed to detonate; and the near-miss 2009 attempt on the life of Saudi Arabia’s intelligence chief.

Photo: U.S. Army

See Also:

• Shadow War in Yemen Could Heat Up After ‘Printer Bomb’ Scare …
• Packing Explosives In Printer Cartridges Fits Qaeda M.O.
• Watch Out, Condé Nast: Al-Qaida Launches English-Language …
• Analyze This: The Mind of the Underpants Bomber
• Drugs, Guns, Remote-Controlled Bombs in Massive Silicon Valley …
• Jam-Proof Insurgents? Doubtful

Authors: Spencer Ackerman

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