Article Photos: Do you know anyone running in Monday's Boston Marathon? 33/44

A Massachusetts state police officer guards the area containing the medical tent, rear, following 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/Josh Reynolds) ORG XMIT: BX103