(CBS/AP) WATERTOWN, Mass. - One suspect in the Boston Marathon bombing is dead and a massive manhunt is on for the other, authorities said early Friday.
In a long night of violence, an MIT police officer was killed, a transit officer was injured in a firefight, and the suspects, who are believed to be brothers, threw explosive devices at police during their getaway attempt, authorities said.
The bombing suspects were identified as 19-year-old Dzhokhar Tsarnaev, of Cambridge, Mass., and his brother, 20-year-old Tamerlan Tsarnaev. Tamerlan Tsarnaev was killed in an exchange of gunfire with police last night.
The suspects are believed to originally from, or near, Chechnya. They are legal permanent residents of the U.S. They are reportedly not students.
Authorities suspended mass transit in Boston and its western suburbs early Friday morning as the massive manhunt continued. All modes of public transportation were also shutdown, including buses, subways, trolleys, commuter rail and boats, said Joe Pesaturo, spokesman for the Massachusetts Bay Transportation Authority.
Residents in Watertown, Newton, Arlington, Waltham, Belmont, Cambridge and the Allston-Brighton neighborhoods of Boston were urged to stay indoors. At least a quarter of a million people live in those suburbs. The notice came as authorities continued to search for Dzhokhar Tsarnaev, the remaining suspect. He is a man seen wearing a white baseball cap on surveillance footage from Monday's deadly bombing at the marathon finish line.
"We believe this man to be a terrorist," said Boston Police Commissioner Ed Davis. "We believe this to be a man who's come here to kill people."
The shutdown came hours after the killing of Tamerlan Tsarnaev, known as the man in the black hat from marathon surveillance footage.
The suspects' clashes with police began only a few hours after the FBI released photos and videos of the two young men, who were seen carrying backpacks as they mingled among marathon revelers. The bombings on Monday killed three people and wounded more than 170 others, and authorities released the images to enlist the public's help finding the suspects.
The images released by the FBI depict two young men, each wearing a baseball cap, walking one behind the other near the finish line of the marathon. Richard DesLauriers, FBI agent in charge in Boston, said the suspect in the white hat was seen setting down a bag at the site of the second of two deadly explosions.
Authorities said surveillance tape recorded late Thursday showed the suspect in the white hat during a robbery of a convenience store in Cambridge, near the campus of MIT. A university police officer was killed while responding to a report of a disturbance, said State Police Col Timothy Alben. The officer died of multiple gunshot wounds.
From there, authorities say, the two men carjacked a man in a Mercedes-Benz, keeping him with them in the car for half an hour before releasing him at a gas station in Cambridge. The man was not injured.
The search for the vehicle led to a chase that ended in Watertown, where authorities said the suspects threw explosive devices from the car and exchanged gunfire with police. A transit police officer was seriously injured during the chase, authorities said.
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."