IEDs hit the U.S. more than you think

There have been 53 publicly known attempted terrorist attacks in the United States since 9/11, and, of those, 43 have been categorized as homegrown plots, according to a government source. Although there is no information publicly available indicating who was responsible for Monday’s attack in Boston, those data show that most terrorist threats in the United States are domestic in origin.

Intelligence and other government officials have said that the Saudi individual currently under guard at a Boston area hospital is not a suspect in the twin explosions that rocked the finish line of the Boston Marathon. Initial reports suggested the individual was a “person of interest,” framing the attack as one that might have emanated or at least been inspired by al Qaeda or another international terrorist group.

But government officials believe that enhanced vigilance in the United States since 2001 has made it more difficult for terrorist networks that are otherwise large and sophisticated enough to have global reach to strike the American homeland. That leaves smaller groups or individuals acting on their own to carry out attacks.

For example, last October, Mohammad Rezwanul Ahsan Nafis was arrested in a plot to bomb the Manhattan office of the Federal Reserve Bank -- an operation reportedly inspired by the memory of Osama bin Laden, who had been killed a year and a half earlier in the raid in Pakistan. In September 2012, the FBI arrested 18-year-old American Adel Daoud in a plot to detonate a car bomb outside a bar in Chicago. And in May 2012 five self-described anarchists were arrested in an alleged plot to blow up a bridge in Cuyahoga Valley National Park in Brecksville, Ohio.

Improvised explosive devices, or IEDs, so popular in places like Iraq and Afghanistan, are often the weapon of choice, offering high impact with cheap, easily obtainable materials.

In the last six months alone, there have been 172 improvised explosive device “incidents” in the U.S. -- some 30 a month. Those incidents range from actual explosions to the controlled detonation of devices that are found before they can go off. Most are fireworks, pipe bombs, pranks, or other “non-terror” related activities, government sources say. American IEDs often consist of a combination of homemade and commercially-available explosives and are triggered by cell phones. Monday’s attack included an IED made out of a pressure cooker packed with explosives. The FBI tracks IED use across the United States.

“If this turns out to be a terrorist attack, it will be the fifth most violent attack in terms of casualties,” said Bill Braniff, executive director National Consortium for the Study of Terrorism and Responses to Terrorism at the University of Maryland. Despite what some people may think, he said, the attack was reasonably sophisticated, with multiple explosive devices. “There is more investment, the more of these explosives you generate,” he said. “So there is a level of patience and planning.”

The top four attacks are, in order, 9/11; the World Trade Center bombing in 1993, which caused 1,048 casualties; the Oklahoma City bombing in 1993, with 818 casualties; and an incident in Oregon in 1984 in which 751 people were sickened by widespread salmonella poisoning at the hands of the Rajneeshis group. There are more than 170 casualties from the Boston attack.

Photo by John Tlumacki/The Boston Globe via Getty Images