Boston Marathon Bombing Kills Three

Boston Marathon Bombing Kills Three
As Boston Marathon runners walk by, SWAT team members stand guard near the finish line 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/Winslow Townson)

Two bombs exploded at the Boston Marathon Monday, killing three people and injuring more than 140. ABC's Aaron Katersky has the latest.