Ottawa runner Shelley Baran holds a sign in tribute to the victims of the Boston Marathon bombings, at the United States Embassy in Ottawa after marching in solidarity with the Boston community on Monday, April 22, 2013.
Lt. Mike Murphy of the Newton, Mass., fire dept., carries an American flag down the middle of Boylston Street after observing a moment of silence in honor of the victims of the bombing at the Boston Marathon near the race finish line.
This file photo provided Friday, April 19, 2013 by the Federal Bureau of Investigation shows Boston Marathon bombing suspect Dzhokhar Tsarnaev.
Massachusetts Institute of Technology police officers march as they depart St. Patrick's Church in Stoneham, Mass., following a funeral Mass for MIT police officer Sean Collier, Tuesday, April 23, 2013. (AP)