Two law enforcement officials say the Tsarnaevs have been living legally in the U.S. for at least one year. Their uncle, Ruslan Tsarni of Montgomery Village, Md., told The Associated Press that the men lived together near Boston and have been in the United States for about a decade.
WATERTOWN, Mass. (AP) -- Two suspects in the Boston Marathon bombing -- identified to The Associated Press as coming from the Russian region near Chechnya -- killed an MIT police officer, injured a transit officer in a firefight and threw explosive devices at police during their getaway attempt in a long night of violence that left one of them dead and another still at large Friday, authorities said.
Residents of Watertown, a suburb just outside Boston, have been advised to keep their doors locked and not let anyone in.
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Hours earlier, police had released photos of the marathon bombing suspects and asked for the public's help finding them.
A law enforcement intelligence bulletin obtained by the AP identified the surviving bomb suspect as Dzhokhar A. Tsarnaev (JOE-khar Tsahr-NEYE-ev), 19, of Cambridge, Mass. His uncle is cooperating with investigators and confirms the two suspects were brothers. Tamerlan Tsarnaev, the second suspect, is dead.
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 while the other escaped.
"We believe this to be a terrorist," Boston police Commissioner Ed Davis said. "We believe this to be a man who came here to kill people."
The FBI said it is working with local authorities to determine what happened.
The MIT shooting on the Cambridge campus Thursday night was followed by reports of gunfire and explosions in Watertown, about 10 miles (16 kilometers) 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.
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In Watertown, witnesses reported hearing multiple gunshots and explosions at about 1 a.m. (0500 GMT) 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. (0230 GMT) 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.
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