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The Boston Globe

Metro

A grim hunt for answers in wake of Marathon attack

Bomb pieces, circuit board found; FBI requests tips

Investigators combing through the grim aftermath of the deadly Boston Marathon terrorist attack have found evidence that timing devices were used Monday to detonate the bombs that ripped through race spectators on Boylston Street, said an official briefed on the investigation.

Working with fragments painstakingly gathered at what is considered the city’s largest-ever crime scene, they also ­determined that the two bombs were probably fashioned from 6-liter pressure cookers, filled with nails and small ball bearings, like buckshot, to increase the carnage, and then hidden in black nylon bags or backpacks and left on the ground. FBI bomb experts at the FBI Academy in Quantico, Va., will try to rebuild the devices from fragments that include a circuit board that indicated the bombs were detonated on a timer, rather than remote control.

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