One of two suspects in the deadly Boston Marathon bombing is dead and a massive manhunt is under way for another, officials said today.
Police have locked down Boston neighbourhoods, shut down public transport, and urged people to stay indoors as they launched a dramatic city-wide search for the white-capped teen suspect Dzhokhar Tsarnaev.
Boston Police say they believe the 19-year-old suspect is an 'armed and dangerous terrorist', as the teenager posted threats online during today's manhunt.
Dzhokhar Tsarnaev is on the run after his brother Tamerlan - the second Boston Marathon bombing suspect - was shot dead after a car chase in the city.
After being pursued by police, he is since said to have posted a message online saying he will 'kill everyone because (police) killed his brother'.
Heavily armed police are currently searching properties in Watertown, near Boston, as the manhunt for Tsarnaev continues.
Here are the most recent developments in Watertown, near Boston, where police are focusing their manhunt:
- The 'white-capped' suspected, said to be 'armed and dangerous' is still at large.
- Boston Police have shut down all public transport into and out of Watertown, a suburb six miles from Boston city centre.
- Armed police combing residential areas in Watertown as we speak, hunting for the suspect.
- Police have urged Watertown residents to stay indoors and not answer the door to anyone unless they know it's police.
- Surviving suspect is Dzhokhar A. Tsarnaev, 19, from Cambridge, Massachusetts.
- Police are searching a flat shared by the two suspects in a suburb of Boston.
- Police officer killedat Massachusett's Institute of Technology named as Sean Collier, 26.
The Middlesex district attorney said the two men are suspected of killing a Massachusetts Institute of Technology police officer on campus late last night, then stealing a car at gunpoint and later releasing its driver unharmed.
Hours earlier, police had released photos of the marathon bombing suspects and asked for the public's help finding them.
A new photo of the suspect on the loose was released later showing him in a grey-hooded sweatshirt. It was taken at a 7-Eleven store in Cambridge, just across the river from Boston.
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 at a hospital while the other escaped.
The FBI said it was working with local authorities to determine what happened.
The MIT shooting on the Cambridge campus was followed by reports of gunfire and explosions in Watertown, about 10 miles (16 kms) west of Boston.
The MIT officer had been responding to report of a disturbance when he was shot multiple times, according to a statement from the Middlesex district attorney's office and Cambridge police. It said there were no other victims.
In Watertown, witnesses reported hearing multiple gunshots and explosions at about 1 am local time today. Dozens of police officers and FBI agents were in the neighbourhood and a helicopter circled overhead.
State police spokesman David Procopio said, "The incident in Watertown did involve what we believe to be explosive devices possibly, potentially, being used against the police officers."
Boston cab driver Imran Saif said he was standing on a street corner at a police barricade across from a diner when he heard an explosion.
"I heard a loud boom and then a rapid succession of pop, pop, pop," he said. "It sounded like automatic weapons. And then I heard the second explosion."
He said he could smell something burning and advanced to check it out but area residents at their windows yelled at him, "Hey, it's gunfire! Don't go that way!"
MIT said right after the shooting that police were sweeping the campus in Cambridge and urged people to remain indoors. They urged people urged to stay away from the Stata Centre, a mixed-use building with faculty offices, classrooms and a common area.
Hours later, MIT, the prestigious university with about 11,000 students, said the campus was clear but the shooter was still on the loose.