BOSTON - Investigators on Tuesday searched for the person or group responsible for planting two bombs at the Boston Marathon finish line that killed three people and wounded more than 100 in the worst bomb attack on US soil since Sept. 11, 2001.
The US Federal Bureau of Investigation led a battery of federal, state and local law enforcement agencies on the case, while critically wounded victims of Monday's blasts fought for their lives and others contemplated a new life as amputees.
The bombs ripped through the crowd at the finish line of the Boston Marathon, shattering the annual civic celebration on the Patriots' Day state holiday while tens of thousands of people packed the street to cheer on the runners.
The two devices using gunpowder as the explosive were packed with ball bearings and other shrapnel to maximize injuries, said a senior law enforcement official briefed on the investigation who declined to be identified because of the sensitivity of the information.
No one has been arrested in the bombing. A White House official said the case would be treated as an act of terrorism but it had yet to be determined whether the attack came from a foreign or domestic source.