The two explosive devices that killed three people and wounded more than 170 at the Boston Marathon were likely pressure-cooker bombs similar to those used in Afghanistan, India, and Pakistan.
The explosives were likely placed in a six-liter pressure cooker, placed in black duffel bags, and left on the ground. The pressure cookers were likely packed with shards of metal, nails, and ball bearings, a law enforcement source told the Associated Press .


