A suspect in the Boston Marathon bombings is dead, while the second suspect is still on the run following a shooting in the suburb of Watertown.
The second suspect is believed to be the man wearing a white baseball cap in images released by the FBI yesterday.
Massachusetts State Police have warned people in the Boston suburb of Watertown not to open their doors.
Police said they would conduct a door-to-door, street-by-street search due to what it called a “fluid situation”.
A massive police operation is under way in Watertown after a university police officer at the Massachusetts Institute of Technology was killed.
Another police officer is said to have been shot and critically injured.
The Middlesex district attorney said the two men are suspected of killing the police officer, 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.
Authorities say the suspects threw explosives from the car as police followed it into Watertown.
The suspects and police exchanged gunfire and one of the suspects was critically injured and later died.
Police say the suspect on the loose is a “terrorist” who “came here to kill people”.
Police officers with weapons drawn, and people wearing FBI and ATF jackets, could be seen in the live videos of the scene.
MIT later said that police had determined that the suspect in the shooting was no longer on campus and that it was safe to resume normal activities.
David Procopio, a spokesman for the Massachusetts State Police, said the motive for the shooting was not known.
He said the investigation would be led by the Middlesex County District Attorney’s Office.
Local television images earlier showed one man lying on the ground surrounded by police officers, however it is not known if he is a suspect in the shooting.
Later, a man was shown being led naked to a police car.