Authorities say one of two suspects in the Boston Marathon bombing is dead and a massive manhunt is underway for another.
Residents of the Boston suburb of Watertown have been advised to keep their doors locked and not let anyone in.
The Middlesex district attorney says the two men are suspected of killing an MIT police officer at the college late Thursday, then stealing a car at gunpoint and later releasing its driver unharmed. Hours earlier, police had released photos of the bombing suspects and asked for the public's help finding them.
Federal agents are zeroing in on how the Boston Marathon bombing was carried out, but there's still no word on who did it and why.
An intelligence bulletin issued to law enforcement and released late Tuesday includes a picture of a mangled pressure cooker and a torn black bag. The FBI says evidence indicates the bomber packed a pressure cooker with explosives, nails and ball bearings and hid it in a back pack. The agency says the second bomb was in a metal container, but there isn't enough evidence to indicate that it was a pressure cooker.