Police and National Guard soldiers stand outside Fenway Park before a baseball game between the Boston Red Sox and the Kansas City Royals in Boston, Saturday, April 20, 2013. (AP Photo/Michael Dwyer)
S.W.A.T. team members stand guard on the campus of Massachusetts General Hospital following an explosion at the finish line of the Boston Marathon in Boston, Monday, April 15, 2013. (AP Photo/Michael Dwyer)
An FBI agent goes door-to-door evacuating residents of Norfolk Street as investigators search for a suspect in the Boston Marathon bombings, in Cambridge, Mass., Friday, April 19, 2013. Two suspects in the Boston Marathon bombing killed an MIT police officer, injured a transit officer in a firefight and threw explosive devices at police during a getaway attempt in a long night of violence that left one of them dead and another still at large Friday, authorities said as the manhunt intensified for a young man described as a dangerous terrorist.(AP Photo/Michael Dwyer)
** FILE ** A firefighter tends to an injured man following an explosion near the finish line of the Boston Marathon in Boston, Monday, April 15, 2013. (AP Photo/Michael Dwyer)
Boston police on bicycles patrol on Commonwealth Avenue following the explosions at the finish line of the Boston Marathon in Boston, Monday, April 15, 2013. Two bombs exploded at the Boston Marathon finish line Monday killing two people and injuring dozens. (AP Photo/Michael Dwyer)
Boston police on bicycles patrol on Commonwealth Avenue following the explosions at the finish line of the Boston Marathon in Boston, Monday, April 15, 2013. Two bombs exploded at the Boston Marathon finish line Monday killing two people and injuring dozens. (AP Photo/Michael Dwyer)
** FILE ** A firefighter tends to an injured man following an explosion near the finish line of the Boston Marathon in Boston, Monday, April 15, 2013. (AP Photo/Michael Dwyer)
Elite female marathoners, front row from left, Rita Jeptoo, Mamitu Daska, Meserat Debele, Tirifi Beyene, Alemitu Begna, Shalane Flanagan, Ana Felix and Sabrina Mockenhaupt compete on the course in Wellesley, Mass., Monday, April 15, 2013. (AP Photo/Michael Dwyer)
Elite mens marathoners including Levy Matebo, left, and Markos Geneti, right, run in the 117th Boston Marathon in Wellesley, Mass., Monday, April 15, 2013. (AP Photo/Michael Dwyer)
