A key component of the bombs used yesterday in the attacks on the Boston Marathon resemble the kind of homemade bomb al Qaeda has encouraged English-speaking terrorists to use.
The Daily Beast has confirmed with U.S. counter-terrorism officials that the bombs placed Monday at the marathon were made from pressure cookers, a crude kind of explosive favored by insurgents in Pakistan and Afghanistan. A recipe for a bomb that uses the pressure cooker was part of the debut issue of Inspire, the English-language online magazine of al Qaeda in the Arabian Peninsula.
While the pressure cooker component is far from definitive proof that Monday’s attack was committed associates of al Qaeda, experts inside and outside of the government say it is nonetheless an important lead for investigators.
“The fact that the pressure cooker was used is a curious and suspicious detail which I have no doubt this will lead investigators to look at whether this was inspired, or motivated by an al Qaeda affiliate,” said Evan Kohlmann, senior partner at Flashpoint Global Partners, a New York based security firm. An article in the summer, 2010 issue of Inspire magazine called “Make a Bomb in the Kitchen of Your Mom,” describes the pressurized cooker as the most effective method for bomb-making. “Glue the shrapnel to the inside of the pressurized cooker then fill in the cooker with the inflammable material,” the article instructs.
The how-to was reprinted in Lone Mujahid Pocketbook, a compendium of tips for the do-it-yourself jihadist placed online this year by al Qaeda in the Arabian Peninsula.
While pressure cooker bombs have become common in Pakistan and Afghanistan, they are still rare for the United States. In July 2011, Naser Abdo, a U.S. army private first class was arrested near Ft. Hood on explosives charges. A copy of the Inspire article on bomb making was found in his home.
“Glue the shrapnel to the inside of the pressurized cooker then fill in the cooker with the inflammable material,” the article instructs.
Experts cautioned that it will take more analysis of the bomb to determine whether the pressure cooker bomb matches al Qaeda’s recipe. The people who will be performing that analysis reside at the FBI’s Terrorist Explosive Device Analytical Center, the government’s most comprehensive database on bomb design.
“In some cases where you have a sophisticated bomb maker who is responsible for a number of bombs, there will be an equivalent of a signature effect,” said Brian Michael Jenkins, a senior adviser to the president of the RAND Corporation and an authority on counter-terrorism. “They cut wires in certain ways, there are idiosyncrasies in how these bombs are designed.”
But Jenkins also said in recent cases most of the bombers are amateurs, attempting an attack for their first time. “We have seen mainly in recent years are essentially one offs,” he said. “A single device made by one individual does not leave a signature.”