Audio Transcript:

Lisa Mullins: The crucial tipoff on the mail bombs apparently came from a suspected member of Al Qaeda. The man had been a detainee at the U.S. prison camp at Guantanamo Bay. He was in Saudi Arabia, and is said to have wanted to return to his home in Yemen. He turned himself over to Saudi authorities and discussed the plot during interrogation. Meanwhile in London today, Prime Minister David Cameron convened a crisis committee to decide Britain's response to the attempted attacks. The BBC's security correspondent Gordon Carrera, he's in London. What is the latest on the response there to the terror threat?

Gordon Carrera: We've had a raft of new security measures revolving around screening of items for cargo, freight, including also some passenger luggage items. Particularly printer cartridges, which of course were used in this attempted plot. Will now be banned from hand luggage for instance, if their over a certain weight. There's also restrictions on freight coming from not just Yemen, but also Somalia because of supposed connections, so the beginnings of a new security regime are coming into place now. But it will require international talks and cooperation to make sure it's uniform and workable around the world.

Lisa Mullins: And one of the other countries is being looked at right now, is Saudi Arabia. And there's a particular reason for that. Tell us what the Saudi connection is here.

Gordon Carrera: Well it's from the Saudi's that the key intelligence tipoff appeared to come in this plot. And the Saudi's appeared to have had a person who was once a member of Al Qaeda, who left it in the last couple of weeks in Yemen, went to the Saudi's and offered up the information about this plot. And that seems to have been the key piece of information. Because a large part of Al Qaeda, in the Arabian peninsula comes from Saudi's even though it's based in Yemen. And including the lead bomb maker who's believe to have been behind these devices. And so Saudi Arabia plays a key role, and its intelligence has been vital, and it's obviously one of the strengths that we've seen in the last few days, is the fact that the intelligence sharing appeared to have worked even if the security screening didn't.

Lisa Mullins: Does that mean that if the Saudi's had not provided the tips that they did, that there was more potential for those bombs to explode? Since the security apparatus did not work?

Gordon Carrera: I think that's absolutely right, I think from what people have said here in London, the devices were viable. They appear to probably have been based on some kind of timer. No one's quite been sure yet when they were designed to explode, and where, but they were certainly viable. And they passed through the initial screening process. So, without that tipoff, it could have been a very different outcome.

Lisa Mullins: So what about, Gordon, the tracking the source of this bomb, it seems as if a lot is known, and as you mentioned, they believe they know the person who built the bomb. How do they know that, and what is the signature, that led them to this particular person.

Gordon Carrera: Yes, I mean there's a lot of focus on Ibrahim Hasan Al-Asiri, who is the prime suspect for making these devices. He is also believed to have been behind the Christmas day attempt, with Umar Farouk Abdulmutallab in Detroit. Also an attack on the Saudi prince, and a number of other events in Yemen and beyond. Bomb makers tend to have signatures, their level of sophistication is normally a good insight into who might be doing it and officials seemed to have seen this individual become more and more sophisticated, more and more ambitious, and looking for different ways of evading the security regime. And that's why he's particularly dangerous, and of particular concern. He may not be the leader of the group, but in some ways he's the most important member if he has this level of sophistication and innovation in bomb making.

Lisa Mullins: What are they doing, Gordon, to make sure that there are no other flights that are either in air or set to take off that might have unaccompanied cargo from Yemen.

Gordon Carrera: Well, we heard today, in London, that there have been extensive checks on any cargo which had already left, before ban took place. These items have been extensively inspected and now there are new bans in place. So I think the hope is that there isn't anything else out there that's in the system already. It's not impossible, and U.S. officials have said they can't rule that out, but clearly they are getting more hopeful that there isn't anything beyond these two packages.

Lisa Mullins: If security failed to find these explosives devices, who's security was it who failed?

Gordon Carrera: Well there are security checks along the way, but most of them start in the place of origin, which is part of the problem when it's Yemen. And many of the initial check on cargo will take where cargo originates. And I think that's one of the key concerns is whether the screening in Yemen, and also from Britain we heard today, in Somalia, is good enough at those airports to find these kind of items. Because often once they're in the system they stay in the system, and they don't get checked again necessarily. Although, in some countries there are different check for trusted carriers who have a different level of security, and that's the case in the UK.

Lisa Mullins: Thank you very much, the BBC's security correspondent Gordon Carrera.