Inside the FBI investigation on the Boston bombing

This is a rush transcript from "On the Record," April 15, 2013. This copy may not be in its final form and may be updated.

GRETA VAN SUSTEREN, FOX NEWS HOST: The FBI teaming with police to track down those responsible for the bombing. So what are investigators looking for? Jeff Lanza is a retired FBI agent. He joins us by phone. Jeff, tell me, what does the FBI do now?

JEFF LANZA, RETIRED FBI AGENT (Via Telephone): Well, it starts with a theory of the case. They really have to determine, you know, who could have done this, who would have done it, whether it's a case of domestic terrorism or it's a case of international terrorism.

VAN SUSTEREN: I don't hear Jeff, but somehow I'm lucky enough I get to hear the control room. I hear the control room talking here at Fox but I can't hear Jeff.

LANZA: Hello.


LANZA: Yes, I'm here. Hi Greta.

VAN SUSTEREN: Oh, hi. Can you tell me, what does -- what do the bomb people do now? How do they investigate this?

LANZA: Well, the bomb people specifically are looking for fragments of that bomb and trying to piece it together to -- to -- to lead them to where that material was purchased. You know, look, the -- the Pan Am 103 bombing was solved based on a piece of material that was smaller than a fingernail, so, although that bomb may have been completely destroyed, the IED device, which is probably what it was -- they're going to be looking for little fragments to put that together. And, in addition, they'll also be looking at surveillance tape, talking to witnesses and trying to figure out who was in the area at that particular time when those bombs were placed in those locations.

VAN SUSTEREN: How do they actually do the sort of reverse engineering on these bomb parts that they collect?

LANZA: Well, the people that do the bomb investigations, both from the ATF, who is involved in this as well, and the FBI. They are pretty experienced and they've seen lots of bombs over the years. And the benefit of having -- if there is a benefit to having any type of war, I mean all the IED devices that we had in Iraq and in Afghanistan, they've got a lot of experience because they've been studying those things so they know what these things are made of and they know what those little fragments were composed of originally or what they -- where they came from originally. So they will be able to effectively try and piece that back together.

And then you go to the point where it was purchased. Where those -- where it came from or where it was purchased if it was done so domestically. And then you just follow it back just like you're following a cash only this time you're following the - the equipment that was used and the materials used to make a bomb.

VAN SUSTEREN: How can you find out where these -- I mean, if a -- if the bomb was blown up, how do you find out where the pieces were purchased?

LANZA: Well, you know, there will be tiny pieces there that they can -- you know, they might not be able to put it back together completely, but they will be able to most likely -- now, I'm talking optimistically here -- most likely put together -- at least get enough of a signature to see what those pieces -- where they came from originally. Like I said, Pan Am 103 - fingernail-sized piece used to solve that -- that attack that brought down an airliner back in 1988. But along with the other evidence as well.

I mean, it's not just going to be forensic. They're going to be looking at witnesses' testimony, witnesses' statements. They're going to be looking at the surveillance video. They'll be looking at any type of information that came in beforehand, any type of intelligence that they have. Do other people know about what happened? And it's not -- probably not just one person that -- that -- that knows about this. So other people have knowledge and they'll be trying through their intelligence sources to figure out who that might be just from an intelligence-gathering standpoint.

VAN SUSTEREN: How about the fact that one was -- one exploded and then a number of seconds later a second one? Does that necessarily suggest that it was staggered and that there was a timing device, that there was a cell phone that detonated? Is there anything you can glean from that at all or is that, at this point, just speculation?

LANZA: Yeah, really don't know at this point. I don't think that has any meaning at this point in time. They probably wanted -- my guess would be they wanted those bombs to go off as closely in time as possible to do the most damage, have the most people affected by that rather than have people start to clear the area. That would lead one to believe that it was done from a -- some sort of device that triggered it, which would be most likely a cell phone that allows you -- cell phone detonators allow you to get a pretty good distance from that -- from that -- from that bomb itself so you don't have to be close by. And so the timing, my guess that they wanted them to go off pretty close in time, but it wasn't exact for them.

VAN SUSTEREN: When you say not close by, I mean, you say they could do it, you know from -- from two cities over -- but I mean, how -- when you say they could do it, you know -- you know two cities over? How -- when you say not close by, a cell phone being the detonator, you know, could you be that remote?


VAN SUSTEREN: Could it be any place?

LANZA: It could be the other side of the world, as long as you have a cell phone network, as long as you've got the number to call. You call the number and that's what causes the bomb to go off, so you can -- as long as you're connected to some network and that device is, yeah, you could be in China.

VAN SUSTEREN: And I suppose that -- I mean, I suspect that that cell phone might be able to be tracked down, assuming it's not one that was not just one of those disposable and just gets tossed away, right?

LANZA: Well, that would be very optimistic if it wasn't one of those ones that was tossed away. The tracked phones, those type of devices are used by drug dealers, mob figures alike to avoid detection. So anybody with any smarts whatsoever would have been had -- would have had one of those devices and it's very, very hard to track that down to the original purchaser.

VAN SUSTEREN: How sophisticated is this setup, I mean, if it is a phone that is a detonator. I mean, we don't know that it is at this point. I mean, it may appear that way. But, you know, that seems rather sophisticated to me but I don't make bombs.

LANZA: Well, you know, there's lots of components to a bomb. First the explosive component, there's a timing device, there's -- there's a detonating device. And in this particular case, if it is a cell phone -- one of the theories, of course -- if it is a cell phone-detonating device, all that is really the electrical charge was causing the -- the detonation. So, you call the cell phone, the ringer goes off, the ringer wire is attached to the bomb detonator, and that's what makes it go off. It's just really as simple as that. It's pure electrical - electrical connections. It's pure bomb mechanics. No big deal. It's just, the phone -- the phone is used to make the detonation start that electrical explosion.

VAN SUSTEREN: Jeff, thank you.

LANZA: You're very welcome, Greta.