WASHINGTON – The two explosions that killed three people and wounded more than 170 Monday in Boston were dramatic, the deadliest bombing in the United States since April 19, 1995, when a truck loaded with fertilizer blew up outside the federal building in Oklahoma City, killing 168. But the method of attack wasn’t particularly surprising to anti-terrorism experts: a homemade bomb that officials refer to as an improvised explosive device.
In fact, in the last six months, 172 IEDs were reported in the United States, according to a government count that an official revealed Tuesday in an answer to questions about U.S. preparedness. The official shared the figures, which were gathered before Monday’s explosion, on the condition that neither the official nor the official’s office be identified.
The official shared information in an email that indicated most American IED attacks were small: “Homemade fireworks, childish pranks and other such non-terror related activities.”
But the information also notes that U.S. officials have long understood the threat, and includes a warning that has been distributed to other agencies: “Expect IED attacks by Homegrown Violent Extremists (HVEs) and individuals to continue throughout the United States. High profile events will present additional targets for HVEs and other individuals.”
The bombs in Boston were more powerful and deadlier than any seen in the United States in years. Even so, initial reports from investigators indicate that they were made using gunpowder or black powder as an explosive, not higher-grade and more-dangerous explosives such as C-4, a military-grade plastic explosive.
The explosives were apparently packed into two pressure cookers, an increasingly popular container for bomb-makers from Pakistan to the United States. A pressure cooker bomb allegedly was discovered in the Killeen, Texas, hotel room of a soldier absent without leave from Fort Campbell, Ky., who later was convicted of plotting a 2011 attack on Fort Hood, Texas.
Officials say that with the growth of Internet instruction videos on bomb making, little stands between someone wanting to make a low-grade weapon and being able to do so.
The use of pressure cookers as bomb shells has become so common that some Internet sites call them “trendy.”
Pressure cookers reportedly were used for bombs during the civil war in Nepal in the 1990s, and they were the method for a series of railcar bombings on July 11, 2006, in Mumbai, India, that killed more than 200 people.