BOSTON (AP) - The bombs that blew up seconds apart at the finish line of one of the world's most storied races left the streets spattered with blood and glass, three dead, including an 8-year-old boy, more than 140 wounded and gaping questions of who chose to attack at the Boston Marathon and why.
Federal investigators said no one had claimed responsibility for the bombings one of the city's most famous civic holidays, Patriots Day. But the blasts among the throngs of spectators raised fears of a terrorist attack.
President Barack Obama was careful not to use the words "terror" or "terrorism" as he spoke at the White House Monday after the deadly bombings, but an administration official said the bombings were being treated as an act of terrorism.
"We will find out who did this. We'll find out why they did this," the president said. "Any responsible individuals, any responsible groups, will feel the full weight of justice."
The Pakistani Taliban, which has threatened attacks in the United States because of its support for the Pakistani government, on Tuesday denied any role in the marathon bombings.
The group's spokesman, Ahsanullah Ahsan, denied involvement in a telephone call with The Associated Press. He spoke from an undisclosed location.
The FBI took charge of the investigation into the bombings, serving a warrant late Monday on a home in suburban Boston and appealing for any video, audio and still images taken by marathon spectators.
The fiery explosions took place about 10 seconds and about 100 yards apart, knocking spectators and at least one runner off their feet, shattering windows and sending dense plumes of smoke rising over the street and through the fluttering national flags lining the route.
Blood stained the pavement, and huge shards were missing from window panes as high as three stories. Victims suffered broken bones, shrapnel wounds and ruptured eardrums.
Roupen Bastajian, a state trooper from Smithfield, R.I., had just finished the race when he heard the explosions.
"I started running toward the blast. And there were people all over the floor," he said. "We started grabbing tourniquets and started tying legs. A lot of people amputated. ... At least 25 to 30 people have at least one leg missing, or an ankle missing, or two legs missing."
At Massachusetts General Hospital, Alasdair Conn, chief of emergency services, said: "This is something I've never seen in my 25 years here ... this amount of carnage in the civilian population. This is what we expect from war."
As many as two unexploded bombs were found near the end of the 26.2-mile course as part of what appeared to be a well-coordinated attack, but they were safely disarmed, according to a senior U.S. intelligence official, who also spoke on condition of anonymity because of the continuing investigation.
WBZ-TV reported late Monday that law enforcement officers were searching an apartment in the Boston suburb of Revere. Massachusetts State Police confirmed that a search warrant related to the investigation into the explosions was served Monday night in Revere, but provided no further details.
Some investigators were seen leaving the Revere house early Tuesday carrying brown paper bags, plastic trash bags and a duffel bag.
Police said three people were killed. An 8-year-old boy was among the dead, according to a person who talked to a friend of the family and spoke on condition of anonymity. The person said the boy's mother and sister were also injured as they waited for his father to finish the race.
Hospitals reported at least 144 people injured, at least 17 of them critically. At least eight children were being treated at hospitals.
Tim Davey of Richmond, Va., was with his wife, Lisa, and children near a medical tent that had been set up to care for fatigued runners when the injured began arriving. "They just started bringing people in with no limbs," he said.
"Most everybody was conscious," Lisa Davey said. "They were very dazed."
The Boston Marathon is one of the world's oldest and most prestigious races and about 23,000 runners participated. The race honored the victims of the Newtown, Conn., shooting with a special mile marker in Monday's race.
Boston Athletic Association president Joanne Flaminio previously said there was "special significance" to the fact that the race is 26.2 miles long and 26 people died at Sandy Hook Elementary School.