President Barack Obama pauses as he begins to speak in the James Brady Press Briefing Room at the White House in Washington, Monday, April 15, 2013, following the explosions at the Boston Marathon. (AP Photo/Charles Dharapak)
Gallery: More photos from Boston explosion
Apr. 16, 2013 @ 01:16 PM
Investigators believe the two bombs that ripped through the crowds at the Boston Marathon, killing three people and wounding more than 170, were fashioned out of pressure cookers and packed with shards of metal, nails and ball bearings.