BOSTON — Investigators appealed to the public Tuesday for amateur video and photos that might yield clues to the Boston Marathon bombing as the chief FBI agent in Boston vowed "we will go to the ends of the Earth" to find whoever carried out the deadly attack.
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, which took place 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 said the bombings were an act of terrorism, but investigators do not know if they were carried out by an international organization, domestic group or a "malevolent individual." He said, "the American people refuse to be terrorized."
On Capitol Hill, Defense Secretary Chuck Hagel called the bombings "a cruel act of terror" and said "a thorough investigation will have to determine whether it was planned or carried out by a terror group, foreign or domestic."
Across the U.S., from Washington to Los Angeles, police tightened security, monitoring landmarks, government buildings, transit hubs and sporting events.
"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" and were interviewing witnesses and analyzing the crime scene.
Gov. Deval Patrick said that contrary to earlier reports, no unexploded bombs were found. He said the only explosives were the ones that went off.
FBI agents searched a home in the suburb of Revere overnight. Authorities gave no details. But investigators were seen leaving a building there early Tuesday carrying brown paper bags, plastic trash bags and a duffel bag.
At a news conference, police and federal agents repeatedly appealed for any video, audio and photos taken by marathon spectators, even images that people 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 also gathered a large number of surveillance tapes from businesses in the area and intend to go through the video frame by frame.
"This is probably one of the most photographed areas in the country yesterday," he said.
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."
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.