Boston police stand watch over wheelchairs used in yesterday's Boston Marathon in Boston Tuesday, April 16, 2013. The bombs that ripped through the Boston Marathon crowd were fashioned out of ordinary... more 
Boston police stand watch over wheelchairs used in yesterday's Boston Marathon in Boston Tuesday, April 16, 2013. The bombs that ripped through the Boston Marathon crowd were fashioned out of ordinary kitchen pressure cookers, packed with nails and other fiendishly lethal shrapnel, and hidden in duffel bags left on the ground, people close to the investigation said Tuesday. (AP Photo/Winslow Townson) less 
1 / 25
Associated Press | Photo By Winslow Townson
Tue, Apr 16, 2013 7:49 PM EDT