Massachusetts State Police warned people in the Boston suburb of Watertown not to open their doors and said they would conduct a door-to-door, street-by-street search due to what it called a fluid situation.

It was not immediately clear what connection the warning may have to the Boston Marathon bombings.

A massive police operation was under way in Watertown after a university police officer at the Massachusetts Institute of Technology was killed and one man was taken into custody in Watertown.

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