Expert thinks Boston bomber may have been trained outside of US

The two bombs that ripped through the crowds at the Boston Marathon, killing three people and wounding more than 170, were fashioned out of pressure cookers and packed with shards of metal, nails and ball bearings, a person briefed on the investigation said Tuesday.

According to a bomb materials expert, pressure cooker containment is not a setup common in the U.S.

“It surprises me and it means something to me,” said University of Rhode Island Professor Jimmie Oxley, in an appearance on KIRO Radio’s Luke Burbank Show. “I think a local bomber might be more likely to use pipe bombs.”

Oxley said she’s seen pressure cookers used in bomb making before, in images from Afghanistan. Similar pressure-cooker explosives have been used in India, Nepal, and Pakistan, according to a July 2010 joint FBI and Homeland Security intelligence report. Also, one of the three devices used in the May 2010 Times Square attempted bombing was a pressure cooker, the intelligence report said.

“It might point to training outside the U.S. because certainly we know, for example, the Times Square bomber and also the fellow that was picked up in New York in September of ’09, I believe it was Najibullah Zazi, both had training and their notes were found from training outside the U.S,” said Oxley. “Even though they were operating on their own, they had training from elsewhere.”

There are a couple reasons people might use a pressure cooker to contain an explosive, Oxley explained. If the explosive material is made up of particles, it will have to have containment of some kind, and also the container itself will become part of the weapon.

“Very few people are harmed by the actual overpressure that your bomb creates because most of them are at a distance from it. But when you have a bomb that’s throwing shrapnel fragmentation, that fragmentation can go quite a ways and that’s what’s causing the majority of your injury.”

Investigators said Tuesday they will go to the ends of the earth to find the person or people responsible for the attack. Oxley said there’s likely a lot of information at the scene that will help.

“I’m sure there’s somebody trying to map where each victim was among other things, to see what evidence is still out there. When those pieces flew, did it get lodged in a building? Is that the critical piece of information?”

Fragments of the cookers and other bomb materials were likely found in nearby objects and in victims. All of that will provide clues for investigators, Oxley said.

“Consider way back in ’88, PAN AM 103, an airplane comes down and debris is scattered for miles, and yet they were able to track where everything came from; the clothing that was in the bag, the timer, all of that, lots of signatures there,” said Oxley.

Federal investigators said no one has claimed responsibility for the Boston Marathon bombings.

Oxley said she believes investigators will find the information they need to uncover the bombs’ origins. The question is just how long it will take.

The Associated Press contributed to this report.

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