In this image from video provided by WBZ TV, spectators and runners run from what was described as twin explosions that shook the finish line of the Boston Marathon, Monday, April 15, 2013, in Boston. Two explosions shattered the euphoria of the Boston Marathon finish line on Monday, sending authorities out on the course to carry off the injured while the stragglers were rerouted away from the smoking site of the blasts. (AP Photo/WBZTV) MANDATORY CREDIT
BOSTON (AP) -- Federal agents zeroed in Tuesday on how the Boston Marathon bombing was carried out -- with kitchen pressure cookers packed with explosives, nails and other lethal shrapnel -- but said they still didn't know who did it and why.
An intelligence bulletin issued to law enforcement and released late Tuesday included a picture of a mangled pressure cooker and a torn black bag the FBI said were part of a bomb.
The FBI and other law enforcement agencies repeatedly pleaded for members of the public to come forward with photos, videos or anything suspicious they might have seen or heard.
"The range of suspects and motives remains wide open," Richard DesLauriers, FBI agent in charge in Boston, said at a news conference. He vowed to "go to the ends of the Earth to identify the subject or subjects who are responsible for this despicable crime."