A police officer for the Massachusetts Institute of Technology has been shot dead at the US university's campus in Cambridge near Boston.
The death was confirmed by authorities, who said no suspects were in custody.
Police and the FBI responded to gunshots heard at Building 32 on the campus. Students have been told to stay indoors and away from the area.
Among those terribly injured by the Boston marathon bombs was a dance instructor. Adrianne Haslet-Davis lost her foot in the explosion.
The mother of the two brothers suspected of carrying out the Boston bombings told ITV News they saw last year's race but are innocent.
Boston's marathon bombing suspect Dzohkhar Tsarnaev was charged with an offence that could lead to the death penalty, if he is found guilty.