In searching for clues about whether the deadly bombing in Boston had roots in the U.S. or overseas, investigators will scrutinize the bombs themselves, the timing of the blasts and similarities to earlier attacks.
Investigators haven’t disclosed whether they believe the bombings are home-grown terrorism or originated abroad. Some indicators suggest the investigation is probably focusing on domestic origins to the April 15 assault that killed three and injured more than 170 near the finish line of the Boston Marathon, said Richard Falkenrath, former New York City police deputy commissioner of counterterrorism.
The involvement of agents from the Bureau of Alcohol, Tobacco, Firearms and Explosives is the “first big clue that investigators are pursuing the possibility that this is an act of domestic terrorism,” he said. “Jurisdictionally, the ATF investigates incidents with origins inside the country as well as the handling and sourcing of explosive materials here.”
As investigators furiously pursue leads, one lesson from past bombings is that initial theories don’t pan out and the path of investigations can swing wildly, said Fred Burton, the former deputy chief of counterterrorism for the Diplomatic Security Service.
“We initially thought the Oklahoma bombing was Hezbollah and the original suspect in Atlanta was Richard Jewell,” the security guard who discovered the bomb at Centennial Olympic Park in 1996, Burton said.
The bombing bears similarities to terror attacks in Israel against buses and cafes almost a decade ago, said Randall Rogan, a communications professor at Wake Forest University in Winston-Salem, North Carolina, who helped crack the Unabomber case.
“This was to draw attention and create a spectacle,” he said.
Still, there are some signs that suggest an overseas perpetrator, said Peter Beering, the former director of public safety in Indianapolis.
“This looks a lot like the improvised explosive devices used elsewhere in the world,” he said.
As they pour over clues, investigators will probably compare the Boston Marathon bombing to similar attacks, some successful, some not, these experts suggested. Among them:
2010: Faisal Shahzad, a former financial analyst, drove a bomb-laden Nissan Pathfinder into New York’s Times Square in a failed attempt to kill and maim. The vehicle, containing a device made of firecrackers, propane tanks and gasoline canisters, was found abandoned on the street as the items smoldered. Shahzad was sentenced to life in prison.
2009: A plot to bomb Manhattan subway lines was stopped just days before execution. Three men who lived in the borough of Queens left New York to join the Taliban in Pakistan, where they were recruited by al-Qaeda. All three were convicted.
2005: A bomb detonated near a packed University of Oklahoma’s football stadium in Norman, killing the bomber and no one else. Joel Henry Hinrichs, a 21-year-old mechanical engineering student, had fashioned an explosive from common household products. The bomb turned out to be unstable. The FBI later concluded there was no evidence Hinrichs was a terrorist.
1996: In an early July morning, a backpack with three pipe bombs encircled by nails exploded in Atlanta’s Centennial Olympic Park during the Olympics, killing one and injuring more than 100. FBI agents searched the home of the security guard who discovered the bomb moments before the blast. Investigators later tied the attack to Eric Rudolph through an analysis of bomb elements, including an alarm clock and steel plate. Rudolph, arrested in 2003, pleaded guilty.
1995: On April 19, a truck loaded with homemade explosives destroyed the Alfred P. Murrah Federal Building in Oklahoma City, killing 168 people and injuring more than 500. Shortly after the explosion, Timothy McVeigh was stopped for driving without a license plate. Evidence tied the bomb to McVeigh and two others, all of whom were convicted. McVeigh was executed in 2001.
1993: A truck bomb designed to topple the north tower of the World Trade Center detonated in a parking garage beneath the building, killing six people and injuring hundreds. A vehicle identification number found on the truck’s axle led investigators to a group of conspirators including mastermind Ramzi Yousef and others, later convicted.
1978-1995: Unabomber Theodore Kaczynski, a former University of California at Berkeley math professor, used mail bombs to kill the three and injure 23 from 1978 and 1995 in a terror campaign against technology. He pleaded guilty in 1998 and is serving a life sentence in a maximum security prison in Colorado.