Police officers aim their weapons Friday, April 19, 2013, in Watertown, Mass. A tense night of police activity that left a university officer dead on campus just days after the Boston Marathon bombings and amid a hunt for two suspects caused officers to converge on a neighborhood outside Boston, where residents heard gunfire and explosions.(AP Photo/Matt Rourke)
Police are locking down some neighborhoods in Boston and its western suburbs as they search for the remaining suspect in the marathon bombings.
Authorities urged residents in Watertown, Newton, Waltham, Belmont, Cambridge and the Allston-Brighton neighborhoods of Boston to stay indoors. All mass transit was shut down and businesses are asked to stay closed.
The announcement Friday morning comes hours after the killing one suspect, known as the man in the black hat from marathon surveillance footage. The man in the white hat is on the loose and police are calling him a "terrorist" who came here "to kill."