The plotters behind last week's unsuccessful mail bombings could not have known exactly where their Chicago-bound packages were when they were set to explode, even after a suspected test run, U.S. officials say.
The communication cards had been removed from the cell phones attached to the bombs, meaning the phones could not receive calls, officials said, making it likely the terrorists intended the alarm or timer functions to detonate the bombs.
"The cell phone probably would have been triggered by the alarm functions and it would have exploded midair," said a U.S. official briefed on the investigation of the bombs taken off cargo planes Friday in England and the United Arab Emirates. This person, like other officials in this story, spoke on condition of anonymity to discuss the case.
The official also said Tuesday that each bomb was attached to a syringe containing lead azide, a chemical initiator that would have detonated PETN explosives packed into each computer printer toner cartridge. Both PETN and a syringe were used in the failed Christmas Day bombing of a Detroit-bound airliner linked to an al-Qaida branch in Yemen.
The Obama administration, which has been monitoring intelligence on possible mail plots since at least early September, was preparing new security rules for international cargo in response to the attempted attack.