One of two bomb suspects dead; Boston suburbs shut down

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Two suspects in the Boston Marathon bombing 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 as the manhunt intensified for a young man described as a dangerous terrorist.

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, still on edge over the attack on the marathon, and its western suburbs, authorities suspended 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.