US police are hunting a suspect in Monday’s deadly Boston Marathon bombing in a small town near the city.

A huge police operation started after an officer was shot dead on a university campus.

One suspect was killed during a car-chase and shoot-out in Watertown, six miles (10km) from Boston.

Another suspect, shown in images from the Boston Marathon wearing a white baseball cap, was on the run in Watertown.

Police said the two men are suspected of killing a police officer on campus at the Massachusetts Institute of Technology (MIT) late on Thursday.

They then stole a car at gunpoint and drove away with the car’s owner still on board.

They later released the driver unharmed.

The men threw bombs and traded gunfire with police before being stopped at Watertown.

One suspect was hit by bullets during the chase and later died, police said.

An office was also critically wounded in the chase.

Police later said they were looking for “suspect number two”, the “white-capped individual”.