The bombs that ripped through the crowd at the Boston Marathon were fashioned out of pressure cookers and packed with metal shards, nails and ball bearings to inflict maximum carnage, a person briefed on the investigation said Tuesday.
The source said the explosives were put in 6-liter kitchen pressure cookers, hidden in black duffel bags and left on the ground. They were packed with shrapnel, the person said.
The person said law enforcement officials have some of the bomb components but do not yet know what was used to set off the explosives.
A doctor treating the wounded appeared to corroborate the person's account, saying one of the victims was maimed by what looked like ball bearings or BBs. Doctors also said they removed a host of sharp objects from the victims, including nails that were sticking out of one little girl's body.
Similar pressure-cooker explosives have been used in Afghanistan, India, Nepal and Pakistan, according to a July 2010 intelligence report by the FBI and Homeland Security. Also, one of the three devices used in the May 2010 Times Square attempted bombing was a pressure cooker, the report said.
"Placed carefully, such devices provide little or no indication of an impending attack," the report said.
Doctors say they removed a host of sharp objects from children and adults injured by the Boston Marathon explosions.
More than 170 people were hurt by the blasts, and doctors on Tuesday detailed some of the injuries, including broken bones, amputated limbs and head injuries.
"We've removed BBs and we've removed nails from kids. One of the sickest things for me was just to see nails sticking out of a little girl's body," said Dr. David Mooney, director of the trauma center at Boston Children's Hospital.
Two children remain in critical condition at the hospital with serious leg injuries. Mooney said that tourniquets applied by emergency responders at the race saved the children's lives.
Doctors at Massachusetts General Hospital also say they removed metal fragments from victims of the two bombs.
Dr. Stephen Epstein of the emergency medicine department at Beth Israel Deaconess Medical Center said he saw an X-ray of one victim's leg that had "what appears to be small, uniform, round objects throughout it — similar in the appearance to BBs."
Massachusetts General treated 31 victims of the bombs. The hospital performed four amputations and at least two more patients have legs that are still at risk of amputation, Dr. George Velmahos said.
AP writers Eileen Sullivan in Washington and Mark Pratt in Boston contributed to this report.