WASHINGTON (AP) – U.S. officials say the plotters behind last week’s unsuccessful mail bombings couldn’t have known exactly where their Chicago-bound packages were when they were set to explode – even after a suspected test run.

Officials say the communication cards had been removed from the cell phones attached to the bombs, meaning the phones couldn’t receive calls. That makes it likely the terrorists intended the alarm or timer functions to detonate the bombs.

A U.S. official brief on the investigation tells The Associated Press that the cell phone “probably would have been triggered by the alarm functions and it would have exploded midair.” The official spoke on condition of anonymity to discuss the case.

The Obama administration is preparing new security rules for international cargo in response to the attempted attack.

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