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The Boston Globe

Nation

FBI unit zeroing in on design of devices

WASHINGTON — FBI bomb technicians poring over hundreds of scraps of metal, nails, wires, and other debris — some surgically removed from bomb victims’ flesh — were closing in Thursday on the design of the explosive devices used in the Boston Marathon attacks, according to officials and forensics experts.

In an effort to trace the source of the components, the Explosives Unit at the agency’s state-of-the-art crime laboratory in Quantico, Va., outside of Washington, was comparing the materials collected from sidewalks, rooftops, gutters, overhangs, and even the soles of victims’ shoes against lab reports generated from thousands of previous blasts around the world, looking for a “bomber signature.”

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