Multiple media outlets, citing unnamed sources, reported Wednesday that a video surveillance camera at a Lord & Taylor department store showed a suspect with a backpack near the marathon finish line. The store is between the sites of the two explosions.
An FBI agent has said investigators found pieces of black nylon from a bag or backpack and fragments of BBs and nails, possibly contained in a pressure cooker.
The bombs were made from ordinary kitchen pressure cookers packed with explosives, nails and ball bearings to inflict maximum carnage, investigators and others close to the case said. But the FBI said nobody had claimed responsibility.
Investigators in white jumpsuits had fanned out across the streets, rooftops and awnings around the blast site in search of clues on Wednesday. They combed through debris amid the toppled orange sports drink dispensers, trash cans and sleeves of plastic cups strewn across the street at the marathon's finish line.
President Barack Obama branded the attack an act of terrorism. Obama plans to attend an interfaith service Thursday in the victims' honor in Boston.
Scores of victims of the Boston bombing remained in hospitals, many with grievous injuries. Doctors who treated the wounded corroborated reports that the bombs were packed with shrapnel intended to cause mayhem. In addition to the 5-year-old child, a 9-year-old girl and 10-year-old boy were among 17 victims listed in critical condition.
The trauma surgery chief at Boston Medical Center says most of the injuries his hospital treated after the marathon bombings were to the legs.
"We have a lot of lower extremity injuries, so I think the damage was low to the ground and wasn't up," Dr. Peter Burke said. "The patients who do have head injuries were blown into things or were hit by fragments that went up."