The twin explosions that savaged the Boston Marathon left behind the shredded remains of a black bag and the mangled metal casing of what was once a kitchen pressure cooker, photographs from the FBI show.
Agents said they understood what had caused the bombing: kitchen pressure cookers packed with explosives, nails and other shrapnel. But they said they still don't know who carried out the attack, or why.
"The range of suspects and motives remains wide open," said Richard DesLauriers, special agent in charge in Boston, at a news conference Tuesday. DesLauriers said the FBI would "go to the ends of the Earth" to identify the people responsible for "this despicable crime."
The FBI sent an intelligence bulletin and images of the blast site evidence to law enforcement officials. The Associated Press obtained them.
The image of the pressure cooker shows a blue-gloved hand holding a twisted metal object about the size of a dinner plate, bent like a crushed soda can. Jagged pieces of metal protrude from what appears to be the rim.
The shredded backpack is shown lying on the street near an off-white road marking.
DesLauriers told news media Tuesday that investigators had found pieces of black nylon from a bag or backpack and fragments of BBs and nails. The items were sent to the FBI laboratory in Quantico, Va., for analysis.