All residents of Boston were ordered to stay in their homes Friday morning as the search for the surviving suspect in the marathon bombings continued after a long night of violence that left another suspect dead.
Boston Police Commissioner Ed Davis made the announcement that the entire city should stay indoors at a news conference where Gov. Deval Patrick said the remaining suspect, described as a dangerous terrorist, was still on the loose.
The developments came after the suspects killed an MIT police officer overnight, injured a transit officer in a firefight and threw explosive devices at police during their getaway attempt, authorities said as the manhunt intensified.
The suspects were identified to The Associated Press as coming from the Russian region near Chechnya, which has been plagued by an Islamic insurgency stemming from separatist wars. A law enforcement intelligence bulletin obtained by the AP identified the surviving bomb suspect as Dzhokhar A. Tsarnaev, a 19-year-old who had been living in Cambridge, just outside Boston, and said he "may be armed and dangerous."
Two law enforcement officials told the AP that Tsarnaev and the other suspect, who was not immediately identified, had been living legally in the U.S. for at least one year.
In Boston, authorities suspended all mass transit and urged people to stay indoors as they searched for the remaining suspect, 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."
Authorities urged residents in Watertown, Newton, Arlington, Waltham, Belmont, Cambridge and the Allston-Brighton neighborhoods of Boston to stay indoors. At least a quarter of a million people live in those suburbs. All mass transit was shut down, and businesses were asked not to open Friday. People waiting at bus and subway stops were told to go home.
The shutdown came hours after the killing of one suspect, known as the man in the black hat from marathon surveillance footage.
All modes of public transportation were shut down, including buses, subways, trolleys, commuter rail and boats, said Joe Pesaturo, spokesman for the Massachusetts Bay Transportation Authority.
The White House said President Barack Obama was being briefed on developments overnight by Lisa Monaco, his assistant for homeland security and counterterrorism.
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 180 others, and authorities revealed 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. 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 known for the white hat during a robbery of a convenience store in Cambridge, near the campus of MIT, where 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.
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.
Watertown resident Christine Yajko said she was awakened at about 1:30 a.m. by a loud noise, began to walk to her kitchen and heard gunfire.