A suspect at the centre of the Boston Marathon bombing is on the run after a major police operation was launched in a city suburb. Officers descended on Watertown on Thursday night (April 18) just days after explosions in Boston killed three people and left over 170 wounded. The suspect wanted by police is pictured here in the white cap. Officers say he is dangerous and has come "to kill". The second suspect, pictured here in the black cap, was shot dead as police pursued the men.