Two bombs blew up seconds apart Monday at the finish line of one of the world's most storied races, tearing off limbs and leaving the streets spattered with blood and strewn with broken glass. Three people were killed, including an 8-year-old boy, and more than 170 were wounded.
A doctor treating the wounded said one of the victims was maimed by what looked like ball bearings or BBs.
Federal investigators said no one had claimed responsibility for the bombings on one of the city's biggest civic holidays, Patriots Day. But the blasts raised the specter of another terrorist attack on U.S. soil.
President Barack Obama was careful not to use the words "terror" or "terrorism" as he spoke at the White House on Monday, but an administration official said the bombings were being treated as an act of terrorism.
"We will go to the ends of the Earth to identify the subject or subjects who are responsible for this despicable crime, and we will do everything we can to bring them to justice," said Richard DesLauriers, FBI agent in charge in Boston. He said investigators had received "voluminous tips," were interviewing witnesses and were analyzing the crime scene.
Gov. Deval Patrick said contrary to earlier reports, no unexploded bombs were found. He said the only explosives were the ones that went off.
Across the U.S., from Washington to Los Angeles, police tightened security, monitoring landmarks, government buildings, transit hubs and sporting events.
The FBI took charge of the investigation, converging on a home in the suburb of Revere on Monday night. Authorities gave no details on the search. Investigators were seen leaving a building there early Tuesday carrying brown paper bags, plastic trash bags and a duffel bag.
They also repeatedly appealed for any video, audio and photos taken by marathon spectators, even images that people think might not think are significant.
"There has to be hundreds, if not thousands, of photos and videos" that might help investigators, state police Col. Timothy Alben said.
Boston Police Commissioner Edward Davis said investigators gathered a large number of surveillance tapes from businesses and intend to go through them frame by frame.
Investigators refused to give any specifics on the bombs and say, for example, where they might have been hidden or whether they were packed with shrapnel for maximum carnage, as is often the case in terror bombings overseas.
But 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." He said it remained to be determined what exactly the objects were.
A European security official said Tuesday initial evidence indicates that the attacks were not the work of suicide bombers.
"So far, investigators believe it was not the work of suicide bombers, but it is still too early to rule it out completely," said the official, who spoke from the United States on condition of anonymity because he was not authorized to speak about the U.S. investigation.
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 bombings.
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 columns of smoke rising over the street. Victims lost limbs and 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."
Massachusetts Gov. Deval Patrick says no unexploded bombs were found and that the only explosives were the ones that went off near the end of the 26.2-mile course.
Eight-year-old Martin Richard 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.
A candle burned on the stoop of the family's single-family home in the city's Dorchester section Tuesday, and the word "Peace" was written in chalk on the front walkway.
Neighbor Betty Delorey said Martin loved to climb the neighborhood trees, and hop the fence outside his home.
At last count, Davis said there were 176 injured people at hospitals, at least 17 of whom are critically injured. At least eight children were being treated at hospitals.
Read the full story about how our local runners escaped injuries in Tuesday's Tribune. Don't take the Tribune? Subscribe now by clicking HERE.