Police say one of two suspected Boston Marathon bombers has been killed in a deadly string of events that unfolded outside Boston beginning late last night.
The suspected bomber that remains on the loose is considered armed and extremely dangerous. He is the suspect seen in the white hat in surveillance photos released by the FBI yesterday.
A law enforcement intelligence bulletin obtained by the AP identified the surviving bomb suspect as Dzhokhar A. Tsarnaev, 19, of Cambridge, Mass.
NBC News says the men are brothers. The AP reports that the men are from the Russian region near Chechnya. (Read more about the suspects.)
The other suspect, has died, has been identified as Tamerlan Tsarnaev, 26.
The FBI said it is working with local authorities to determine what happened last night and early this morning.
Police say it began with the suspects robbing a 7-Elevel, then shooting and killing a MIT police officer.
(Read more about the sequence of events.)
The MIT shooting was followed by reports of violence in nearby Watertown, about 10 miles west of Boston.
The MIT officer had been responding to report of a disturbance Thursday night 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 a.m. Friday. Dozens of police officers and FBI agents were in the neighborhood 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 10:30 p.m. 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 Building, a mixed-use building with faculty offices, classrooms and a common area.
Hours later, MIT, which has about 11,000 students, said the campus was clear but the shooter was still on the loose.
Boston is on full lockdown as law enforcement searches for the suspect.
(Information from the Associated Press was used in this report.)