BOSTON — 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, a person briefed on the investigation said today.
The details on the apparently crude but deadly explosives emerged as investigators appealed to the public for amateur video and photos that might yield clues, and the chief FBI agent in Boston vowed "we will go to the ends of the Earth" to find those responsible.
A person who spoke on the condition of anonymity because the investigation was still going on said that the explosives were put in 6-liter pressure cookers, placed in black duffel bags and left on the ground. They were packed with shrapnel to inflict maximum carnage, 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.
At the White House, meanwhile, President Barack Obama said that the bombings were an act of terrorism but that investigators do not know if they were carried out by an international organization, domestic group or a "malevolent individual."
He added: "The American people refuse to be terrorized."
Across the U.S., from Washington to Los Angeles, police tightened security, monitoring landmarks, government buildings, transit hubs and sporting events. Security was especially tight in Boston, with bomb-sniffing dogs checking Amtrak passengers' luggage at South Station and transit police patrolling with rifles.
"They can give me a cavity search right now and I'd be perfectly happy," said Daniel Wood, a video producer from New York City who was waiting for a train.
Similar pressure-cooker explosives have been used in Afghanistan, India, Nepal and Pakistan, according to a July 2010 joint FBI and Homeland Security intelligence report. Also, 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.
The two bombs blew up about 10 seconds and around 100 yards apart yesterday near the finish line of the storied, 26.2-mile race, tearing off limbs, knocking people off their feet and leaving the streets spattered with blood and strewn with broken glass. The dead included an 8-year-old boy. An Amesbury woman is among the injured.
Richard Barrett, the former U.N. coordinator for an al-Qaida and Taliban monitoring team who has also worked for British intelligence, said the relatively small size of the devices in Boston and the timing of the blasts suggest a domestic attack rather than an al-Qaida-inspired one.