A Boston Marathon bombings ' suspect has died in hospital after sustaining critical injuries in a car - chase and shootout with police, as authorities engage in a manhunt for a second suspect.

Boston police officials said on Friday that the manhunt continues for a second suspect who is still at large and possibly armed and dangerous, US media reported.

“We believe this to be a terrorist, ” said Boston Police Commissioner Ed Davis, adding, “We believe this to be a man who came here to kill people. ”

The two suspects were armed with explosives and guns as they battled law enforcement officers in the Boston suburb of Watertown early Friday morning. Authorities say the suspects hurled explosives from a stolen car as they fled a swarm of police officers who exchanged gunfire. “The incident in Watertown did involve what we believe to be explosive devices possibly, potentially, being used against the police officers, ” said a police spokesperson. Two bombings in Boston on Monday left three people dead and more than 170 injured. The two men are also suspected of killing a Massachusetts Institute of Technology police officer on campus late Thursday. The campus police officer was shot multiple times while responding to a report of a disturbance at the prestigious school ' s Cambridge campus.