Yesterday, U.S. agencies confirmed that the CIA had thwarted a new underwear bomb plot from an Al Qaeda group in Yemen, but assured everyone that the public wasn't in danger. Now here's the reason why the U.S. was confident: The bomber was actually a double agent. According to the LA Times, "Saudi Arabia’s intelligence agency, working closely with the CIA, used an informant to pose as a would-be suicide bomber. His job was to convince the Al Qaeda franchise in Yemen to give him a new kind of non-metallic bomb that the militants were designing to easily pass through airport security."

The NY Times reports:

In an extraordinary intelligence coup, the agent left Yemen, traveling by way of the United Arab Emirates, and delivered both the innovative bomb designed for his air attack and critical information on the group’s leaders to the C.I.A., Saudi and other foreign intelligence agencies.

After spending weeks at the center of the terrorist network’s most dangerous affiliate, Al Qaeda in the Arabian Peninsula, the agent provided critical information that permitted the C.I.A. to direct the drone strike on Sunday that killed Fahd Mohammed Ahmed al-Quso, the group’s external operations director and a suspect in the bombing of the American destroyer Cole in Yemen in 2000.

The Times adds, "A senior American official said the device was sewn into “custom fit” underwear that would have been very difficult to detect even in a careful pat-down." The official said that there were two ways for the bomb to be set off and it would have "undoubtedly would have brought down an aircraft."

It's believed the bomb was designed by Ibrahim Hassan Asiri, who intelligence officials believe is in Yemen. And the reason why the U.S. government waited to announce the plot was because they were trying to get the agent and his relatives to secure places. Former White House counter-terrorism advisor Richard Clarke told ABC News, "It's quite an accomplishment to be able to pass yourself off as an al-Qaeda terrorist to the terrorists, when in fact you're working for a US or allied intelligence agency... By having the bomb in its original state, before it goes off, U.S. experts are now able to figure out how the bomb works, how it might be detected. That's a heck of a lot easier when the bomb is still intact, than after it's exploded and you're picking up pieces."

But, as ABC News' Brian Ross points out, "Still, there is great concern that [al-Asiri] is working on other bomb designs, including bombs surgically implanted in terrorists, even picture frames and radios, as shown in an al Qaeda video from 2009... American authorities said today that as long as Asiri is alive, making other bombs for real terrorists, there remains a grave threat to the U.S."