CBS News senior correspondent John Miller is a former assistant director at the FBI and former head of the Counterterrorism and Criminal Intelligence Bureau and the Major Crimes Division of the Los Angeles Police Department.

(CBS News) The would-be bomber in the recently-uncovered plot to blow up a U.S.-bound airliner leaving Yemen was an undercover intelligence agent. The plot was revealed to U.S. intelligence officials based on a tip by Saudi intelligence services, and had been revealed by a Saudi intelligence source who had been inside Al Qaeda in the Arabian Peninsula and providing information to the Saudis and the CIA for some time.

The double-agent revelation goes right to the heart of an intelligence agency's nightmare, which is identifying a source that they've placed inside an organization.

Intelligence agencies and senior officials tell CBS News they're not going anywhere near commenting on the issue for obvious reasons.

The Associated Press is reporting that the alleged double agent has been removed from Yemen and apparently is safe. This may go a long way toward explaining why authorities said yesterday that the bomber was no longer considered a threat.

It may well be that he was actually working with the CIA all along.

Since 2009, U.S. intelligence officials have had a laser focus on AQAP - al Qaeda in the Arabian Peninsula - the group most believe is responsible for the latest bomb plot.

It's a highly capable group made up of experienced leaders, battle tested terrorists and a very talented bomb maker.

This latest plot serves as a stark reminder of their primary mission: bring down an American plane.

A former FBI agent who has questioned more members of AQAP tells CBS News that what makes AQAP - of all the al Qaeda affiliates - the chosen one to attack America is that they are the closest to Osama bin Laden's version al Qaeda. That's why they feel it is their duty, their obligation to continue the bin Laden fight, regardless of what other al Qaeda groups do in different areas.

Ibrihim al-Asiri is AQAP's master bomb maker. When the group's leaders plotted to kill Saudi Arabia's counterterrorism chief at his home in Jeddah in 2009, Asiri made the bomb and personally chose the suicide bomber: his own brother.

That gives some idea about the dedication and the level of hatred that the group has. The Saudi counterterrorism chief survived; Asiri's brother did not.

But Asiri continued to make bombs that were cleverly disguised; the underwear bomb that failed to detonate on board a jetliner over Detroit on Christmas, 2009, and two bombs hidden in printers that were shipped as cargo through U.P.S. and Fed-Ex. The printer bombs were intercepted by intelligence agents just hours before they were set to blow up the planes that carried them.

Bomb technician Kevin Barry says he sees in Asiri's work increasing in "sophistication at trying to prevent being detected."

"They're making mistakes," adds Barry. "They're not big mistakes. But we've been fortunate that they've been caught."

Barry says Asiri's bombs reveal a bit about the man.

"It tells you that he has the assets, he has the intent, and he has no conscience," Barry says.

Now the FBI has Asiri's most recent bomb at their lab in Quantico, Virginia. What they're doing now is working on reverse engineering it.

They're going to actually make and blow up a copy of the bomb. They're going to learn how it worked, how it would function, and what effect it would have on an aircraft in flight.