April 2013 Boston Marathon Bomb

Boston Marathon

This two image combination photograph shows Rita Jeptoo, of Kenya, left, and Lelisa Desisa, of Ethiopia, right, crossing the finish line to win the women's and men's division of the 2013 running of the Boston Marathon in Boston, Monday, April 15, 2013. (AP Photo/Charles Krupa)

APTOPIX Boston Marathon Explosions

People react as an explosion goes off near the finish line of the 2013 Boston Marathon in Boston, Monday, April 15, 2013. Two explosions went off at 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 Boston Globe, David L Ryan)

Boston Marathon Explosions

Police officers react to a second explosion at the finish line of the 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 Boston Globe, John Tlumacki)

APTOPIX Boston Marathon Explosions

In this photo provided by The Daily Free Press and 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)

Boston Marathon Explosion

A Boston police officer clears Boylston Street following an explosion at the finish line of the 2013 Boston Marathon in Boston, Monday, April 15, 2013. Two explosions shattered the euphoria at the 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/Charles Krupa)

Boston Marathon Explosions

Women react as they walk from the area where there was an explosion after the Boston Marathon in Boston, Monday, April 15, 2013. (AP Photo/Josh Reynolds)

Boston Marathon Explosion

A Boston police officer wheels in injured boy down Boylston Street as medical workers carry an injured runner following an explosion during the 2013 Boston Marathon in Boston, Monday, April 15, 2013. Two explosions shattered the euphoria at the marathon's 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/Charles Krupa)

APTOPIX Boston Marathon-Explosions

An unidentified Boston Marathon runner is comforted as she cries 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)

Boston Marathon-Explosions

Two Boston Marathon volunteers hug each other, at right, as an injured person is loaded into an ambulance 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)

Boston Marathon Explosions

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. Two bombs exploded near the finish line of the marathon on Monday, killing at least two people and injuring at least 23 others. (AP Photo/Winslow Townson)

Boston Marathon-Explosions

Boston police patrol near the finish line of the Boston Marathon following an explosion in Boston Monday, April 15, 2013. (AP Photo/Winslow Townson)

Boston Marathon Explosions

Chris Darmody, right, holds his wife Sue in Boston, Monday, April 15, 2013. Chris says he was waiting for Sue when an explosion detonated near his location at the finish line of the Boston Marathon. The couple were later reunited after all runners were diverted from the course. (AP Photo/Michael Dwyer)

Boston Marathon-Explosions

One of the blast sites on Boylston Street near the finish line of the 2013 Boston Marathon is investigated by a person in a protective suit in the wake of two blasts in Boston, Monday, April 15, 2013. (AP Photo/Elise Amendola)