In Boston, a violent night unfolds

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    How we arrived at the manhunt

How we arrived at the manhunt 01:41

Hours after the FBI released images of two suspects in the Boston Marathon attack, the hunt for the suspects shifted into high gear.

Massachusetts State Police spokesman Col. Timothy Alben said the violence started when a convenience store was robbed late Thursday.

Soon after, in Cambridge, across the Charles River from Boston, a Massachusetts Institute of Technology police officer was fatally shot while he sat in his car, the Suffolk County District Attorney's Office said in a statement. Police say they think the bombing suspects were responsible for the shooting.

Authorities say they believe the two hijacked a car at gunpoint in Cambridge and released the driver a half-hour later at a gas station.

As police gave chase, the car's occupants threw explosives out the windows and shot at officers, according to the district attorney's office.

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    Police: 1 suspect dead, 1 on the run

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    Witness: We heard explosions, gunshots

Witness: We heard explosions, gunshots 01:28

Officers fired back, wounding one of the men, the person apparently identified by the FBI as "Suspect No. 1." That man died at Beth Israel Hospital. He had bullet wounds and injuries from an explosion, according to officials. The second man apparently escaped.

Richard H. Donohue Jr., 33, a three-year veteran of the transit system police force, was shot and wounded in the incident and taken to a hospital, a transit police spokesman said Friday. The officer's condition was not immediately known.

    Police have been engaged in a massive manhunt for the suspect Friday morning.