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

Photo by: David L. Ryan

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