He described how he had had to cower for several hours in 100-degree heat when a drone circled above. "That day was bad ... it's a nasty situation to be in, man," chipped in Khalid.

Khalid described how the drones restricted movement for fighters in the region: "They were restricted to one place most of the time: One place to eat, sleep, go to toilet and do everything."

Terror training on UK soil

Naseer and Khalid implemented the new al Qaeda strategy when they returned to the United Kingdom. Just days before their arrest on September 18, 2011, Naseer provided Ashik Ali, the third Birmingham man convicted Thursday, with hands-on instruction in how to make explosives.

According to expert witnesses consulted in the trial, Naseer had acquired the correct knowledge to teach recruits how to make viable bombs. The recordings suggested their planned attacks were still months away.

In one of the bugged conversations, Naseer is heard suggesting that the restrictions on training in Pakistan meant it was just as effective training recruits in the West.

"[In the tribal areas] you get bit of an experience in fighting -- but you know the rest of the stuff that could be taught -- they taught us in a room."

At one point, Naseer warned Ali that if he hit or rubbed the explosives in a certain way it could explode and potentially kill him; just one of the many lessons he passed on from his training in Waziristan.

In the days before their arrest, Naseer experimented and tinkered with potential bombmaking chemicals in a Birmingham home, including the chemicals inside sports injury cold packs. The recordings revealed that his instructors in Pakistan had taught him that ammonium nitrate- - a potentially high powered explosive -- could be extracted from such packs, demonstrating al Qaeda's continued inventiveness.

Pantucci told CNN the Birmingham case illustrated that despite intensified drone strikes in Pakistan, Western militants were still finding ways to connect with al Qaeda in the region, providing the terrorist groups opportunities to attack the West.

He said al Qaeda's new emphasis on training Westerners to in turn provide terrorist instruction in the West reflected the group's looser control over plots than just a few years ago.

Unlike the 7/7 bombers, and other recent terrorist conspiracies like a plot to attack Manchester in 2009, the Birmingham plotters do not appear to have been in touch with their handlers in Pakistan after returning to the United Kingdom.

Pantucci says the pressures on al Qaeda have resulted in a shift toward a new model of "fire and forget."

The March 2012 Toulouse terrorist shootings provided further evidence of looser control by al Qaeda of terrorist plots in the West. The perpetrator of the attack -- Mohammed Merah -- was encouraged by the group to return to France to launch an attack during a short stay in the tribal areas of Pakistan in September 2011 but planned every aspect of the operation himself, including which targets to strike.