Fox News chief intelligence correspondent Catherine Herridge reports that the bombs used in the Boston Marathon attack did not rely on cell phone detonators, using a "line of sight" speed controller from a remote control toy car as the trigger. It is not known what the range is on the specific controller that was used, but it is typically 250 yards or less.

The national security source, who spoke on condition of anonymity, said it is believed one or both of the brothers used the controllers to detonate the bombs, but the involvement of a third person to trigger the devices still has not been ruled out.

Herridge said there is no evidence of a third suspect at the scene, but investigators are poring over the Tsarnaev brothers' computers in an attempt to learn more.

She said it's also significant that this bomb-making process is not part of the Al Qaeda propaganda magazine Inspire, which contains how-to information on bomb-making.


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