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 Tuesday.
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, 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.
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"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 said they removed metal fragments from victims of the 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."
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.
Federal investigators said no one had claimed responsibility for the bombings.
Massachusetts Gov. Deval Patrick said despite earlier reports, no unexploded bombs were found at the Boston Marathon. He said the only explosives were the two that went off Monday.
Patrick said while other parcels were checked, no other bombs were found.
Early Tuesday morning, police officers carried several large bags from a suburban Boston apartment that authorities say was searched in connection to the Boston Marathon bombing. A law enforcement official who spoke on condition of anonymity because he was not authorized to release details of the investigation said the man had been tackled by a bystander, then police, as he ran from the scene, but he said it is possible the man was simply running away to protect himself from the blast, as many others did.
The explosions took place about three hours after the winners crossed the finish line but while many runners were still crossing the finish line. The bombs detonated 10 seconds and around 100 yards apart.
The crime scene is being called the most complex crime scene in the history of the Boston Police Department, according to Police commissioner Ed Davis.
Investigators said there were security sweeps in the area before the blasts.
Special Agent in Charge Richard DesLauriers said at a news conference Monday morning that there are no known additional threats and the bombing remains a very active investigation. ATF officials said explosives specialists are being brought in to assist in the investigation including explosives-detecting canines.
The law enforcement representatives also repeatedly appealed for any video, audio and photos taken by marathon spectators, even images that people think might not be significant.
"There has to be hundreds, if not thousands, of photos and videos" that might help investigators, state police Col. Timothy Alben said.
Davis said investigators gathered a large number of surveillance tapes from businesses and intend to go through them frame by frame.
The Boston Marathon is one of the world's oldest and most prestigious races and about 23,000 runners participated. Most of them had crossed the finish line by the time the bombs exploded, but thousands more were still completing the course.
The attack may have been timed for maximum bloodshed: The four-hour mark is typically a crowded time near the finish line because of the slow-but-steady recreational runners
completing the race and because of all the friends and relatives clustered around to cheer them on.
According to the race's website, 521 Colorado residents were registered to race Monday. So far, there is no information indicating any of them were injured in the explosions.
"All of a sudden, it made a really bad explosion, like a boom," said Junko Kazukawa, a runner from Denver who had just left the medical tent when the explosion occurred.
Lucy West, a runner in the marathon from Broomfield, told 7NEWS she was about a half mile from the finish when the blasts occurred. She borrowed a stranger's cellphone to tell her husband she was unhurt.