Seattle Police officers, including Craig Williamson, center, and his explosives detection dog, "Dennis" confer as during a patrol in downtown Seattle, Monday, April 15, 2013, in reaction to explosions at the Boston Marathon finish line earlier in the day. A Seattle Police blog posting said that although there was no indication of a direct threat to Seattle, officers would be increasing patrols and activity around the city. (AP Photo/Ted S. Warren)
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.