Thomas, bringing us an exclusive interview with attorney general Eric holder. The attorney general sounding an alarm about how this conflict could intensify the terror threat at home. It really is... See More
Thomas, bringing us an exclusive interview with attorney general Eric holder. The attorney general sounding an alarm about how this conflict could intensify the terror threat at home. It really is George. As the conflict intensifies, between Israel and hamas, holder says he'll be on the lookout for any hint of violence here at home. That potential and what is happening in Syria makes for an especially dangerous moment. We met the attorney general in London after a series of urgent meetings about the threat from Syria. Do they share your sense of urgency about Syria? There's a great concern about this Syrian foreign fighters problem. About 7,000 of them right now in Syria. Coming from Europe, from the United States. And great concern about the impact they're having there but the potential impact they could have in their home countries. Congressman Rogers, made a comment recently that he had not seen a situation where there was so many threat streams so active at one moment. Perhaps since 9/11. I think we are at a dangerous time. Reporter: Moments later, as we sat together, he laid out his concerns in detail. You sounded the alarm about Americans and europeans going to Syria. Is this a clear and present danger? I think it is. In some ways, more frightening than anything I have seen as attorney general. 9/11 came out of the blue. This is a situation that we can see developing and the potential that I see coming out. The negative potential I see coming out of the facts in Syria and Iraq, now, are quite concerning. Reporter: Among the concerns, intelligence that bombmakers from Yemen, those responsible for the 2009 underwear bomb plot are now in Syria joining forces with the thousands of foreign fighters there. Is that a particularly nasty mix? It's a deadly combination. You have people that have the technical no-how and a fervor to give their lives in support of a cause directed at the united States and directed at its allies. And, it's something that gives us really extreme, extreme concern. Reporter: Sources tell ABC news U.S. Intelligence suspects that Yemeni bombmakers in Syria have designed a device small enough to fit in a laptop computer. It's why the U.S. Asked foreign countries to step up security. We're constantly monitoring what is going on out there. What known bombmakers are doing. The new techniques they're trying to employ. Reporter: Suffice it to see these security upgrades we're seeing didn't come out of the blue? No. They're not things that we decided, it's July. Let's do something new. This is not a test. We're doing something in reaction to things that we have detected. Reporter: Americans who have gone into Syria and made their way home. How many people are under surveillance inside the united States? I would say dozens of investigations that are under way. The FBI is on top of it. Reporter: And another challenge. Isis. The islamic state of Iraq and Syria. They have taken over huge chunks of Iraq. They have allegedly confiscated low-grade radioactive material that could be used for a dirty bomb. How concerned should Americans at home be about Isis? Well, I think, at this point, Isis is a body concerned about doing things in Iraq and Syria. If they're able to consolidate gains in that area, it's a matter of time before they start looking outward. And start looking at the west. And at the United States in particular. So this is something we have to get on top of and get on top of now. Reporter: Is there a sense of resurgence with Al Qaeda? The Al Qaeda core has certainly been diminished. As we have been saying for some time, other factions are stronger. Groups that were once part of Al Qaeda and have now split from them are stronger. Reporter: The administration scored a victory with the capture of Ahmed Abu khatala. One of the alleged planners on the awe salt on the U.S. Consulate in benghazi that killed U.S. Ambassador Chris Stevens and three others. Even that has been controversial. He was having lunch in public, being interviewed by journalists. What say you to that? I think that is really an argument I don't understand. It's one thing to talk to a reporter and have your face not even shown on camera while you're doing this. It's a whole other thing to come to the custody of the FBI, the United States military. I don't think that he would have had a cup of coffee with a couple of FBI agents or members of our military. Reporter: He's being held in the U.S. Under tight security. Facing trial in Washington. A number of republicans on the hill said he should be in interrogation on a military ship. He should be headed to a military court not civilian court. There's not a tension in the way we have done this and getting intelligence that can be useful. And then ultimately convicting this person. I think it's time for us to get beyond this point. Now it's become something that I think is purely political and totally inconsistent with the facts. Reporter: The job of national security can be relentless. Not only does holder have to worry about overseas threats, he also has to worry about home-grown radicals, like the two men that allegedly attacked the Boston marathon last year. Is that threat any less serious? Those lone wolves. The home-grown violent extremists keep me up at night as well. Trying to monitor them. Trying to anticipate what it is that they're going to do. The experience we had in Boston is instructive. It takes only one or two people to do something horrific. And Pierre, the attorney general, you talked to him about homegrown terrorists motivated by domestic concerns. Yes. We recently had a case of someone assaulted on the courthouse steps in Georgia. Two officers killed near las Vegas. That is coming back, as well. May be a resurgence. He said there are a lot of sleep less nights these days.
This transcript has been automatically generated and may not be 100% accurate.