We came to Yemen shortly after the attempted bombing, retracing Abdulmutallab's life, visiting the school where he came to study Arabic.
This is the third floor room where Abdulmutallab spent most of his time while he was at the institute here in Yemen. Just a bed, a desk, a closet.
But officials say it was not Arabic he was studying here. He was training at Al Qaida camps outside Sana'a, and building bombs with the direct help of the American Awlaki.
MICHAEL CHERTOFF, FORMER HOMELAND SECURITY SECRETARY: Getting Americans who understand the culture, understand the way Americans think, and potentially have the ability to come back to the U.S. with clean papers, that is the ultimate weapon for Al Qaida in terms of being successful.
RADDATZ: U.S. Special Forces are now training thousands of Yemeni troops in counterterrorist techniques to go after Al Qaida, and the U.S. has launched an aggressive campaign of its own. In the last year, there have been at least half a dozen ship-launched cruise missile strikes here, targeting training camps and Al Qaida leadership. But the man they are really after has eluded them. The man many U.S. officials believe is likely behind this latest terror plot.
For "This Week," I'm Martha Raddatz.
AMANPOUR: We're joined now by the assistant to President Obama for homeland security and counterterrorism, John Brennan. Thank you for joining us.
BRENNAN: Good morning, Christiane.
AMANPOUR: Do you believe that there are any more explosives-laden packages out there, or just the two that we intercepted?
BRENNAN: We can't presume that there are none other that are out there, so what we're trying to do right now is to work very closely with our partners overseas to identify all packages that left Yemen recently and to see whether or not there are any other suspicious packages out there that might contain these IEDs.
AMANPOUR: So, is this threat still active? Is it neutralized?
BRENNAN: It is a very active investigation that is ongoing. We can't presume, again, that we have identified all of the packages that are out there. We need to make sure that we get to the bottom of this, understand who was behind it and what else might we be facing.
AMANPOUR: The woman who is in custody, is she the prime suspect?
BRENNAN: The Yemenis have announced that the two individuals, a woman and her daughter, are the individuals presumed to have delivered those packages to the FedEx and UPS offices in Sana'a. And so we're working very closely with the Yemenis. They're questioning those individuals right now. We're hoping to get the results of those questions soon.
AMANPOUR: Do you think there was somebody else involved, or those women deliberately did that?
BRENNAN: I think the sophistication of these IEDs shows, at least in my mind, that it was an Al Qaida in the Arabian Peninsula effort, and that there are a number of people that are involved in this. And so it's not just these two individuals. We're looking for a lot more.
AMANPOUR: Are you looking for the 28-year-old bombmaker Hasan al-Assiri (ph), who also is apparently alleged to have made the bomb of the underwear bomber on Christmas Day?