Anatomy of a pressure cooker bomb

This is a rush transcript from "On the Record," April 16, 2013. This copy may not be in its final form and may be updated.

GRETA VAN SUSTEREN, FOX NEWS HOST: For more on the lethal bombs, retired FBI bomb technician Kevin Miles joins us. Kevin, let me sort of jump in. We're trying to figure out how this investigation is going to get solved, and I think that this bomb -- these bombs are really going to help identify the killer or killers.

Is it possible that from those -- from the pieces of that bomb that there may have been some DNA that was deposited from the handling of them that could still be on those bomb parts?

KEVIN MILES, DIRECTOR OF TROY ASYMMETRIC/FORMER FBI SPECIAL AGENT BOMB TECHNICIAN: Absolutely. I used to teach a class before I retired two months ago from the FBI, and in that class, I made all the students aware of the fact that there is no such thing as vaporization. All the components in both of those devices are out there on that crime scene someplace. Quite a few of them will probably have some DNA, if the bomber was dumb and left the DNA there. Sometimes, they know more about DNA than we do. But if he left DNA, it will survive these detonations, remarkably.

VAN SUSTEREN: Is it almost impossible not to leave DNA? I guess you could assemble it with gloves or something. But I would think that it would be almost virtually impossible to be DNA free.

MILES: I mean, if you're forensically pure. Most criminals are not forensically pure. They will leave something at the crime scene. They'll leave something on the IED. Years ago in Afghanistan, I worked a bombing and I collected all the evidence and I sent I back to the lab. And I never saw what they recovered. They recovered an eyelash from the evidence that I sent them. And they examined that eyelash, got DNA off of it, and found the suspect, who was already in jail in Afghanistan.

So it does happen. It's tough to be completely forensically pure in these sorts of situations. So hopefully, we'll get lucky out there.

VAN SUSTEREN: All right, well, and that's probably what they're doing tonight. All right, let me turn to now the bomb itself. You know, if this bomb were handed to you as your project, what would you do to try to begin to sort of do reverse engineering or try to identify anything that might lead to the killer? What would you do?

MILES: Well, what they're going to do, what they're doing right now, is they're going to collect all the evidence. I mean, even if -- if it's foreign to the scene, if it's not supposed to be there on that street, they're going to pick it up.

And at the very end of this crime scene, Boylston is going to be spotless. Every bit of dust and dirt is going to be taken from those scenes. They'll send it back to the lab. The lab personnel over the course of a few weeks will put that entire device back together again. And what's going to happen, hopefully, within the next couple of weeks or more.

VAN SUSTEREN: If you find some pellets or nails in there, and that -- can you -- can you figure out where they were purchased from? Can you be that precise?

MILES: That's going to be tough. A ball bearing is a ball bearing most of the time. However, the FBI lab I know for a fact has every component, every switch, every ball bearing, every nail, every battery known to mankind in a registry. If it's a ball bearing been made someplace in Taiwan or Thailand, they're going to have it. And if it's intact in fairly good shape, they'll compare it, and hopefully, get a match.

VAN SUSTEREN: Is there any particular part that you would look at, whether it's something to do with the detonation or anything that's sort of a signature that would help you -- you know, that would lead you to the person? Anything at all? I mean, do some bomb makers, you know, create the same look in the bomb or they use the same materials? Is there anything unique about a bomb?

MILES: Yes, they do. I used to build bombs for a living in the FBI, and I would use one certain switch on almost every single one of them. And I was known for that. This particular individual, since there are two devices, if they were built by the same person might have a signature, as well, that will help the investigators identify who it was.

Sometimes, however, there is no signature. And that just happens. It's in the course of the bomb builder's imagination.

VAN SUSTEREN: As best we can piece together -- and we've actually put the pictures of the bomb parts that we have -- we put it on People can go look at them. But as best as we can -- as you can figure out, how much do you think it costs to make one of these bombs?

MILES: Well, it depends on what kind of explosives that were used. I do not know for sure. Like I said, I'm only two months removed from the bureau, and I'm not about to contact these guys behind me, whom I all know -- who I know every one of them who are on the scene right now.

It's a possibility there are low explosives involved in this situation, and low explosives are relatively available, homemade explosives. I'm hesitant to guess on how much. But I've heard a hundred bucks. It's probably going to be a little bit more than that. If you put all the precursors together and nails that have been mentioned, the -- and whether a kind of switching mechanism, which we've not heard yet, it's probably not going to be not a lot of money involved at all.

VAN SUSTEREN: How long would it take you to build one of these bombs?

MILES: Well, I don't know exactly what's been in there. But -- you know, I never built real bombs. But if -- it would probably take me no more than an hour, maybe less, to put one of these things together.

VAN SUSTEREN: So if someone were building a bomb around you, like, you know, what -- I mean, you'd probably see someone go to a hardware store, someone would be -- I mean, I -- I mean, what are sort of the things that -- you know, if you knew a bomb builder, what would you sort of -- if he lived in your building, what would you sort of notice, anything?

MILES: Not really. There really is nothing that obvious about somebody walking in with a pressure cooker and a day later walking in with a box of nails, and a day after that, walking in with a box of ball bearings. It really doesn't arouse any kind of suspicion.

VAN SUSTEREN: All right, Kevin, thank you. I've got complete confidence they're going to find this killer, and I think this bomb is going to lead -- give us lots of clues. Thank you, Kevin.

MILES: You bet.