One of the blast sites on Boylston Street near the finish line of the 2013 Boston Marathon is investigated by two people in protective suits in the wake of two blasts in Boston Monday, April 15, 2013. (AP Photo/Elise Amendola)
Runners who were diverted from the race course walk on the Commonwealth Mall two blocks from the site of an explosion at the finish line of the Boston Marathon in Boston, Monday, April 15, 2013. Two bombs exploded near the finish line of the Boston Marathon on Monday, killing at least two people and injuring at least 23 others. (AP Photo/Michael Dwyer)Medical workers aid injured people at the finish line of the 2013 Boston Marathon following an explosion in Boston, Monday, April 15, 2013. (AP Photo/Charles Krupa)Medical workers aid injured people at the finish line of the 2013 Boston Marathon following an explosion in Boston, Monday, April 15, 2013. (AP Photo/Charles Krupa)An unidentified Boston Marathon runner leaves the course crying near Copley Square following an explosion in Boston Monday, April 15, 2013. (AP Photo/Winslow Townson)Medical personnel work outside the medical tent in the aftermath of two blasts which exploded near the finish line of the Boston Marathon in Boston, Monday, April 15, 2013. (AP Photo/Elise Amendola)People react to an explosion at the 2013 Boston Marathon in Boston, Monday, April 15, 2013. Two explosions shattered the euphoria of the Boston Marathon finish line on Monday, sending authorities out on the course to carry off the injured while the stragglers were rerouted away from the smoking site of the blasts. (AP Photo/The Daily Free Press, Kenshin Okubo)People react to an explosion at the 2013 Boston Marathon in Boston, Monday, April 15, 2013. Two explosions shattered the euphoria of the Boston Marathon finish line on Monday, sending authorities out on the course to carry off the injured while the stragglers were rerouted away from the smoking site of the blasts. (AP Photo/The Daily Free Press, Kenshin Okubo)Firefighters tend to a man following an explosion 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 at least two people injuring dozens. (AP Photo/Michael Dwyer)One of the blast sites on Boylston Street near the finish line of the 2013 Boston Marathon is investigated by two people in protective suits in the wake of two blasts in Boston Monday, April 15, 2013. (AP Photo/Elise Amendola)Justine Franco of Montpelier, Vt., holds up a sign near Copley Square in Boston looking for her missing friend, April, who was running in her first Boston Marathon Monday, April 15, 2013.