Boston police news conference
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Boston police: Marathon bomb suspect 'armed and dangerous'

A major police operation is under way following the fatal shooting of an officer at the Massachusetts Institute of Technology (MIT) which is being linked to the bombings at the Boston marathon on Monday.

Speaking at a news conference, police told residents to remain in their homes and not open their doors.

Police confirmed 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

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