ONE of the suspects in the Boston Marathon bombing is dead but another man is on the run after a massive manhunt.
A tense night of police activity in the area has left a university officer dead on campus just days after the bombings amid the hunt for two suspects, with residents hearing gunfire and explosions.
The chaos in Watertown, about 10 miles west of Boston, occurred just hours after a Massachusetts Institute of Technology police officer was shot and killed on campus. It was unclear if the outbursts of violence were related.
A transit officer has also reportedly been treated at a local hospital for gunshot wounds in relation to the chaos.
The Boston police commissioner has confirmed to reporters that one of the suspects is dead but another is on the run, apparently holed up in a building.
A 20-block perimeter has been established as authorities search for him.
The Boston police scanner told officers they were searching for a white male, with a gray hoodie and dark curly hair, armed with an assault rifle and possible explosives.
He is believed to the suspect wearing a white hat, seen in surveillance footage released today.
Below are images of two suspects in the Boston bombings
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