Boston Marathon Bombings: Explosives made of pressure cookers, placed in black duffel bags, source says

(CBS/AP) BOSTON - Sources said Tuesday that the explosives that killed three and wounded more than 170 people at the Boston Marathon were made of pressure cookers packed with metal and ball bearings. President Barack Obama said it was unclear whether the bombings were carried out by an international organization, domestic group or a "malevolent individual."

PICTURES: Explosions near Boston Marathon finish line

President Barack Obama, speaking to reporters at the White House, said it was unclear whether the bombings were carried out by an international organization, domestic group or a "malevolent individual."

A person briefed on the attack spoke to The Associated Press under condition of anonymity that the explosives were in 6-liter pressure cookers and placed in black duffel bags that were placed on the ground. The person said the duffel bags contained shards of metal, nails and ball bearings.

These types of pressure cooker explosives were used in Afghanistan, India, Nepal and Pakistan, according to a July 2010 joint FBI and Homeland Security intelligence report. One of the three devices used in the May 2010 Times Square attempted bombing was a pressure cooker, the intelligence report said.

"Placed carefully, such devices provide little or no indication of an impending attack," the report said.

The Pakistani Taliban, which claimed responsibility for the 2010 attempt in Times Square, has denied any role in the Boston Marathon attack.

Richard DesLauriers, FBI agent in charge in Boston, said earlier that investigators had received "voluminous tips" and were interviewing witnesses and were analyzing the crime scene.

Police said three people were killed, including 8-year-old Martin Richard who was with his family near the finish line. The boy's mother and sister were both seriously injured.

Police commissioner Ed Davis said 176 victims were brought to hospitals around Boston, and 17 were in critical condition. At least eight children were being treated at hospitals.

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