BOSTON - Two bombs exploded in the packed streets near the finish line of the Boston Marathon on Monday, killing three people and injuring more than 140 in a terrifying scene of shattered glass, bloodstained pavement and severed limbs, authorities said.
WCVB, the ABC affiliate in Boston, reported that police and federal agents were searching an apartment at 364 Ocean Ave. in Revere, Mass. on Monday evening with a possible connection to the explosions. It is unclear what led them to that location.
A person familiar with the situation told The Associated Press that an 8-year-old-boy was killed in the explosions.
Someone who spoke to a friend of the family and spoke to the AP on condition of anonymity to protect the family's privacy confirmed that an 8-year-old boy was among the dead.
The person said the boy's mother and sister were also injured as they waited for his father to finish the race.
MORE IMAGES: Explosions rock Boston Marathon
Eight hospitals reported that they are treating at least 124 people. Of those, at least 15 are in critical condition.
Authorities announced a third person died as a result of the explosions during a Monday evening press briefing.
An emergency room doctor at Massachusetts General Hospital told ABC News that they have performed several amputations, particularly on victims whose legs were injured. Many of the victims are runners still wearing numbers on their shirts, the doctor said.
He described the injuries as "shrapnel-type wounds" as possibly caused by "pipe bombs," though police have not confirmed that description.
Dr. Richard Wolfe, chief of the department of emergency medicine at Beth Israel Deaconess Medical Center, says one or two of the hospital's 21 patients faced a "high probability of mortality."
Earlier, trauma nurse from Massachusetts General Hospital told ABC News that medical workers had set up a temporary morgue at a medical tent at the road race and were treating patients with severed limbs and children with severe burns.
A former Army medic said the scene was "more like Baghdad and Bombay than Boston."
Bruce Mendelsohn was attending a post-race party in an office building just above the blast site when an explosion knocked him to the floor. He rushed outside and found blood, glass and debris everywhere, and began applying pressure to what he calls "gruesome" wounds.
Boston Police Commissioner Edward Davis said a fire at the JFK Library did not appear to be related to the two blasts near the finish line of the Boston Marathon.
Authorities said the explosion at the JFK Library happened about an hour after the other blasts, and Davis said there are no injuries stemming from the third explosion.
Davis urged people to stay indoors and not congregate in large groups.
Police say they received no information before the explosions to indicate they were coming.
Bloody spectators were being carried Monday to the medical tent that had been set up to care for fatigued runners.
One of the runners described a gruesome scene inside a medical tent near the finish line, as bombing victims were brought in "with no limbs." He says he tried to shield his children's eyes, but says "they saw a lot."
Police wove through competitors as they ran back toward the course.
"There are a lot of people down," said one man, whose bib No. 17528 identified him as Frank Deruyter of North Carolina. He was not injured, but marathon workers were carrying one woman, who did not appear to be a runner, to the medical area as blood gushed from her leg. A Boston police officer was wheeled from the course with a leg injury that was bleeding.
About three hours after the winners crossed the line, a loud explosion happened on the north side of Boylston Street, just before the photo bridge that marks the finish line. Another explosion could be heard a few seconds later.
One woman says she was waiting for her husband to cross the finish line, and, in her words, "it just blew." She described it as "a loud boom, and then glass everywhere." Cherie Falgoust says something hit her head, and she "just ducked."
A runner, Laura McLean of Toronto, says she heard two explosions outside the medical tent. She says, "There are people who are really, really bloody." McLean says, "they were pulling them into the medical tent."
A runner said, "There are a lot of people down."
Terrorism expert Glen Winn believes the timing between the two explosions may have been intentional to cause maximum casualties.
After clearing the crowds, Winn says police will now comb the area looking for the tiniest of clues.
"Everything has been left in place, the bloodied sidewalks, the trash, everything's left," said Winn. "There might be a small piece of… initiator that really tells a story on both of them. OK, this was made by the same person, they used the same wiring."
Cellphone companies say service is operating in the Boston area, but with heavy traffic following of the explosions at the Boston Marathon.
A law enforcement official, citing an intelligence briefing, said cellphone service had been shut down Monday in the Boston area to prevent any potential remote detonations of explosives.
But officials with Verizon Wireless and Sprint Nextel said there had been no such requests.
Sprint spokeswoman Crystal Davis said: "Minus some mild call blocking on our Boston network due to increased traffic, our service is operating normally."
Obama: 'We will find out who did this'
President Barack Obama, responding to the explosions at the Boston Marathon, says the United States does not know "who did this or why" but vowed that whoever is responsible "will feel the full weight of justice."
He said: "We will find out who did this and we will hold them accountable."
Obama made his remarks Monday evening from the White House about three hours after two explosions detonated near the marathon's finish line. At least two people were killed and 50 injured in the blasts.
Obama has been in touch with federal law enforcement and Massachusetts officials in the aftermath of the explosions.
The Secret Service reacted cautiously to the blasts, expanding the security perimeter around the White House.
Full Justice Dept. resources probing Boston bombs
Attorney General Eric Holder has directed the full resources of the Justice Department be deployed to investigate the bombs that exploded at the Boston Marathon.
A department official said Holder has spoken with FBI Director Robert Mueller and with Carmen Ortiz, the U.S. attorney for Massachusetts. The official said Ortiz's office was coordinating the department's response with the FBI and other federal, state and local law enforcement authorities.
The official spoke on condition of anonymity because she was not authorized to speak on the record.
2 nuke plants tighten security after Boston blasts
Nuclear power plants in Massachusetts and New Hampshire have increased security after two bombs exploded in Boston on Monday, killing at least two people and injuring dozens. The Pilgrim Nuclear Power Station in Plymouth, Mass., and the Seabrook Station in Seabrook, N.H., heightened checks of vehicles, materials and individuals entering the plants.
Pilgrim, about 45 miles south of Boston, was already shut down for refueling when the explosions occurred. Seabrook is about 45 miles north of Boston in Seabrook, N.H.
Eliot Brenner, a spokesman for the Nuclear Regulatory Commission, said federal officials have not ordered changes in security at other U.S. nuclear reactors in the wake of the Boston explosions.
Secret Service expands security at White House
The Secret Service says it has expanded its security perimeter at the White House following the explosions at the Boston Marathon.
Secret Service spokesman Ed Donovan says the measure was taken "out of an abundance of caution." He says it is not unusual to expand or contract the security perimeters.
Shortly after the explosions Monday, Secret Service shut down Pennsylvania Avenue outside the White House, cordoning off the area with yellow police tape. Several Secret Service patrol cars also blocked off the entry points to the road.
The White House was not on lockdown and tourists and other onlookers were still able to be in the park across the street from the executive mansion.
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