The two suspects were identified by law enforcement officials as brothers from Chechnya. The surviving suspect was identified as Dzhokhar A. Tsarnaev, 19, of Cambridge, Mass., a law enforcement official said. The one who was killed was identified as his brother, Tamerlan Tsarnaev, 26. The authorities were investigating whether the dead man had an improvised explosive device strapped to his body when he was killed, two law enforcement officials said.
. . . .
Col. Tim Alben of the Massachusetts State Police said investigators believed that the two men were responsible for the death of Massachusetts Institute of Technology police officer and the shooting of an officer with the Massachusetts Bay Transportation Authority, . . . .
. . . .
About 10:30, police received reports that a campus security officer at M.I.T. was shot while he sat in his police cruiser. . . .
A short time later, police received reports of an armed carjacking of a Mercedes sport-utility vehicle by two males in the area of Third Street in Cambridge, . . .
The police immediately began to search for the vehicle and pursued it into Watertown. During the chase, “explosive devices were reportedly thrown from car by the suspects,” the statement said, and the suspects and police exchanged gunfire in the area of Dexter and Laurel streets.
. . . .