Marathon explosives prepared from pressure cookers

BOSTON - The explosives that killed three and injured more than 170 at the Boston Marathon were made of pressure cookers filled with metal and ball bearings, a person briefed on the investigation said Tuesday.

These types of pressure cooker explosives have been 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 statement said.

Placed carefully, such devices provide little or no sign 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.