A second explosion goes off (rear) as a runner was blown to the ground by the first explosion near the finish line of the 117th Boston Marathon. (Photo by John Tlumacki/The Boston Globe via Getty Image)
President Barack Obama committed the full resources of the federal government to the investigation of the deadly twin bombings at the Boston Marathon and he pledged to hold the perpetrators accountable.
"We still do not know who did this or why," Obama said in a televised statement from the White House just over three hours after the explosions that killed three people and injured more than 100. "But make no mistake: we will get to the bottom of this. And we will find out who did this." Whoever is responsible "will feel the full weight of justice."
US spy agencies had no advance warning of an impending attack, said Senate Intelligence Chairwoman Dianne Feinstein and two other intelligence officials, who asked for anonymity to discuss the investigation.
The blasts were the first mass-casualty bombing in the US since the Sept. 11 attacks. Federal investigators were immediately dispatched to the scene to begin combing through video of the scene from multiple cameras and examine debris from the explosion for forensic clues. Police were examining other potential devices found in the area. They were not believed to be explosives, according to two federal law enforcement officials.
Several people were being questioned, including a foreign national in the country on an expired student visa who is not classified as a suspect at this point, according to a federal law enforcement official. Boston police have no suspect in custody, Commissioner Ed Davis said at a news briefing.
The attack is being treated as a terrorist act because it involved multiple explosive devices, though investigators have not yet found any link to an organized terror group, foreign or domestic, said a White House official who asked for anonymity. Obama did not use the term terrorism in his televised remarks.
Federal law defines terrorism as violence to "intimidate or coerce" either the government or members of the public, according to the FBI website. The site chosen for the explosions, near the finish line of the race, provided maximum opportunity for television exposure.
Local police confiscated mobile phones from people in the area of the explosion, said Michael McCaul, a Texas Republican who is chairman of the House Committee on Homeland Security. Insurgents in Iraq sometimes use cellphone signals to detonate bombs.
Obama cautioned that people "shouldn't jump to conclusions before we have all the facts."
US intelligence agencies had no prior indications that any foreign group was planning an attack in the US today, said two US officials with access to classified reports of international communications, satellite imagery and other material that sometimes provides warnings of possible foreign terrorist acts.
A third official, who wasn't authorized to speak publicly, said among the considerations is the timing of the attack. It came on the day when federal income taxes customarily are due and Patriots' Day in Massachusetts, celebrating the opening shots of the American Revolution against the British Crown, which might point to a domestic extremist group.
Obama said security across the country would be stepped up "as necessary" in response to the attack. The Secret Service restricted pedestrian access in front of the White House "out of an abundance of caution," said Edwin Donovan, a spokesman for the Secret Service.
The blasts at the race, which attracts about 25,000 runners and 500,000 spectators each year, follow several bombing attempts since the Sept. 11 terrorist attacks in 2001.
Quazi Mohammad Rezwanul Ahsan Nafis, a 21-year-old man from Bangladesh, pleaded guilty in February to planning to bomb the New York Federal Reserve last year.
In 2010, Faisal Shahzad was sentenced to life in prison for driving a car containing an explosive into New York's Times Square, and Najibullah Zazi pleaded guilty to supporting al- Qaeda and plotting in 2009 to attack New York subways.
Nor was yesterday's attack the first bombing of a major U.S. sporting event.
A blast at Centennial Olympic Park in Atlanta, Georgia, on July 26, 1996, killed one and injured more than 100 people. Eric Robert Rudolph, an anti-abortion activist, admitted detonating the 40-pound pipe bomb.
Investigations into bombings like the pair of explosions near the finish line of the Boston Marathon are typically run by a Joint Terrorism Task Force, a partnership of law enforcement and investigative agencies ranging from state and local police departments to the FBI to the US. Immigration and Customs Enforcement, according to former government officials involved in such probes.
The oldest task forces, commonly referred to by their initials, JTTF, date back to the 1980s and currently number more than 100 nationwide, including one in the Boston area, according to Shawn Henry, a former executive assistant director of the FBI.
"It'll be all hands on deck. Everybody working their areas of responsibility," said Henry, referring to the initial effort to collect evidence and interview witnesses in the bombings.
"Investigators will be checking with their sources, looking at video feeds that might be available, talking to people who set up the course, seeing if they might have noticed something unusual," said Henry, president of CrowdStrike Services, an Irvine, California-based security consultant. Authorities can't automatically assume the bombings are the work of Islamist terrorists, who have been linked to several bomb plots since the Sept. 11 attacks, Henry said.
"It could be somebody who's got a grievance," Henry said, adding that yesterday was the day federal taxes are due. "It could be someone who doesn't like paying taxes."
Philip Mudd, former deputy director of the CIA's Counterterrorist Center and a former senior intelligence adviser to the FBI, said investigators will be studying the style of the bombings, which based on what currently is publicly known, do not bear the classic marks of al Qaeda-inspired attack plots.
Those efforts have sought to inflict maximum casualties in crowded iconic locations, like New York's Times Square, or its subway system, Mudd, director of global risk at SouthernSun Asset Management in Memphis, Tennessee, said.
"Here you have what appears to be a relatively small bomb in a public place that's not iconic," Mudd said.