The bombs that tore through a crowd of spectators at the Boston Marathon could have cost as little as $100 to build and were made of the most ordinary ingredients — so ordinary, in fact, that investigators could face a gargantuan challenge in attempting to use bomb forensics to find the culprit.
Investigators revealed Tuesday that fragments recovered at the blast scene suggest a simple design: a common pressure cooker of the kind found at most discount stores, packed with an explosive and armed with a simple detonator. A final ingredient — a few handfuls of BBs, nails and pellets — helped ensure widespread casualties when the two devices exploded Monday near the race's finish line, law enforcement officials said.
The devices' design was immediately recognized by counterterrorism experts as a type touted by al-Qaida for use by its operatives around the world. Similar devices have been used by terrorists in mass-casualty bombings in numerous countries, from the Middle East to South Asia to North Africa.
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