6:55 AM ET:  The AP is reporting that the suspects are from Chechnya, and have lived in the US for at least one year. The surviving Boston bomb suspect has been identified as Dzhokhar Tsarnaev, 19, of Cambridge, Ma. [AP] NBC News is reporting that both suspects are brothers. Sources say that the men may have military experience, according to law enforcement officials.

6:30 AM ET: CNN is reporting that officials are worried that the suspect who remains at large could have explosives on his body. An official tells the network that the suspect killed overnight had explosives on his body.  As a result, city officials have suspended all public transportation for the time being. Those in Watertown and the surrounding neighborhoods are being urged to shelter in place until further notice. Many colleges have cancelled classes for the day.  Businesses are being told not to open.  [Boston Police & CNN]

4:24 AM ET: At a very brief press conference this morning, police announced that a suspect wanted in the Boston Marathon bombing was killed during an early-morning standoff in Watertown, Ma. One suspect remains at large. Boston Police Commissioner Ed Davis said of the at-large suspect: "We believe he is a terrorist, we believe he is out there to kill people."

Police officials also confirmed that a transit police officer was severely wounded during the Watertown standoff.

Police are advising Watertown residents to stay in their homes. They're continuing to search a twenty block radius for the suspect.

4:15 AM ET: Boston Police confirm they have apprehended one suspect and tweeted a picture of a second suspect:

@Boston_Police WANTED: Police Searching for Suspect (Picture Provided) pic.twitter.com/3jY9kwOTbj

Federal and local officials faced off with two assailants less than five miles outside of Boston early this morning in connection with a carjacking and a series of explosions in the streets of Watertown, Mass.

Police officials say this incident is related to Monday's Boston Marathon bombings. Boston Police Commissioner Ed Davis tweeted "One suspect dead. One at large. Armed and dangerous. White hat suspect at large."

Just after 10 p.m. on Thursday, a police officer was shot to death on MIT's campus in Cambridge.

In a statement, a representative from the college said, "MIT police have determined that the suspect in this evening’s shooting is no longer on campus. It is now safe to resume normal activities." The college, however, will be be closed on Friday.

Television reporters on the scene in Watertown said they saw FBI agents and Homeland Security officials on the scene, but that has not been confirmed.

Police remain on the scene, and according to TV station WBZ TV, may be looking for a second suspect.

This story will be updated as soon as more details become available.

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