ROBERT SIEGEL, HOST:
From NPR News, this is ALL THINGS CONSIDERED. I'm Robert Siegel.
MELISSA BLOCK, HOST:
And I'm Melissa Block.
One day after the bombings at the Boston Marathon, a large team of investigators is searching for answers. And there are many questions about the bombs themselves.
For more on the forensic investigation, I'm joined by former FBI Special Agent Frank Doyle Jr. He worked on a number of bombing investigations, including the World Trade Center, Oklahoma City, the Atlanta Olympics and the Unabomber case. Frank Doyle, welcome to the program.
FRANK DOYLE JR.: Thank you.
BLOCK: Well, as investigators are on the streets of Boston gathering clues, walk us through what they're collecting, what specifically they're looking for.
DOYLE: Well, of course, they're looking for any item of evidence that might lead them to the structure of the device, any component piece. These are very difficult investigations because you have first responders and civilians flocking in to help all of the injured. And the downside of that is that they are trampling evidence. They are maybe embedding component parts in their soles of their shoes and carrying it away with them.
I know investigators will be going to the hospitals and talking with the doctors and the surgeons, requesting any foreign items that may have been embedded in the victims and recovering all of that. So the immediate goal will be trying to identify any of these pieces of evidence. And, of course, probably hundreds of hours spent screening all of the videos available, all of the pictures that were taken, and just trying to digest what happened here.
BLOCK: You mentioned going to hospitals. I know doctors at the hospitals in Boston have talked about removing shrapnel and nails from the victims. So investigators will want to look at those, and what conclusions would they draw?
DOYLE: Well, it - when you mention nails or any kind of shrapnel, that clearly defines the intent of the perpetrator to cause bodily injury when these become flying projectiles, more or less just like bullets, where it's designed to maim and injure innocent peoples. So that's a significant indication.
BLOCK: Mr. Doyle, as you've seen the video and listened to the sound of these bombs from yesterday, is there anything that you can tell about the power or the composition? For example, you see a cloud of white or sort of gray smoke from the first explosion, does that tell you anything?
DOYLE: Well, typically, but not absolute. As you saw a large cloud of somewhat white or gray smoke, that is typically indicative of a nonmilitary explosive, more of a commercial explosive. Most of the military explosives, a lot of them are petroleum-based, and thus you get a darker, shall we say, black cloud of smoke. But again, that's not absolute. So that would be a clue.
You saw a large fireball there. The device - I kind of backed off a little bit when I heard some of the terminology used as a crude device. Well, crude, no. It functioned well. It killed three so far. And I think the number's up around 13, 14 still critical. So the bomber achieved his goal. It was sophisticated enough to work.
BLOCK: Frank Doyle Jr. is a former special agent with the FBI. Mr. Doyle, thanks for your time.
DOYLE: Glad to talk with you.
BLOCK: And a brief recap of what we do know about the bombs: Investigators say they believe the bombs were contained in pressure cookers - common kitchen devices - packed with explosives, blasting caps, ball bearings and nails. The bombs were likely set off using timers. This afternoon, the FBI said scraps of black nylon were found at the scene. They may have come from backpacks or bags where the bombs were hidden. Transcript provided by NPR, Copyright NPR.