While the Guantanamo Bay terrorist prison recidivism rate (over 25 percent) regularly makes the news you rarely (and for good reason) hear about those freed from Guantanamo who have been “turned” (into informants against their terrorist colleagues). Getting Guantanamo prisoners to talk is a well-known activity there. Less well known are efforts to convince some of these hard-core terrorists to switch sides. Even before September 11, 2001, counter-intelligence experts had discovered that it was very difficult to get agents into Islamic terrorist organizations. Since then, it's become easier. But the process is difficult, and very dangerous for those who agree to go undercover in these terrorist organizations. So far, Islamic terrorists and the public know a few dozen. Two of the most prominent double agents came from Guantanamo. There was Abdul Rahman, an Afghan, who was released, returned to terrorism in Pakistan and was found out as a double agent and killed by his terrorist associates. Another Islamic terrorist, a Saudi Arabian (Jabir Jubran Al Fayfi), was one of more than a hundred Saudi inmates released from Guantanamo in 2006-2007. He returned to Saudi Arabia where he went through a mandatory rehabilitation course. There he was apparently recruited by Saudi intelligence. Once out of rehab Fayfi went to Yemen and joined the al Qaeda organization. He made it back to Saudi Arabia in 2010 with all sorts of useful information. This included news of the printer toner cartridge plot that was disrupted (and failed) at the end of October 2010. It’s still unclear of Fayfi was a double agent or just someone who turned after being arrested again.
Indications are that there are apparently a lot more (perhaps hundreds) such agents out there. Most of these you will have to wait a long time to find out about. Even the details of the recruiting process are top secret, in order to protect the agents recruited, and make it more difficult for the wrong people (potential double agents) to be hired. But the process tends to work best on those who have become disillusioned with Islamic radicalism. There are a lot of these men, but most simply walk away. Others wish to fight against the cause they lost faith in. All the Americans had to do was get hip to the cultural buttons, and learn how to push them. Apparently the Israelis helped with this, as the Israelis have long run extensive informant networks in Arab populations. The Israelis have a thick playbook, and the U.S. apparently got them to share. Some NATO nations (especially the French) have useful experience to add to this. Several NATO nations are known to regularly turn Islamic terrorists and use them as informants.
There are plenty of prospects. Every man (and some women) arrested as suspected terrorists are potential agents. There are 600 men released from Guantanamo, along with over 100,000 arrested in Iraq, Afghanistan and elsewhere. As long as these suspects were in custody recruiting attempts went forward. Many potential spies were willing to work with the Americans, but not the local (Iraqi or Afghan or whatever) government. The Americans were considered more reliable, and the Americans could get you out of your native country (perhaps even to America) if you delivered.
Guantanamo, on the other hand, was a more difficult place for recruiting. A quarter of 598 terrorism suspects released from Guantanamo are known to have returned to Islamic radical activities. Others were suspected of doing so. This was not a big surprise, except for the extent of the recidivism. There had long been reports of men released from Guantanamo backsliding. Before the Guantanamo revelation, Saudi Arabia announced that at least 12 percent (of 117) of Saudis released from Guantanamo Bay returned to terrorist activities. Saudi Arabia said it would either rehabilitate, or keep jailed, those released from Guantanamo Bay. Thus the admission that 14 of these men returned to terrorism was embarrassing. What the Saudis have not been able to talk about is how many of those Saudi citizens released were recruited to become spies inside al Qaeda.
Aside from the recruiting, the rehab program has been a success. Many young men who were leaning towards a life of terrorism, responded to some good attitude adjustment. But this reminds the Saudis that the hard core will just go through the motions. The Saudis continue to have problems with "rehabilitated" terrorists returning to terror. But they consider it an acceptable cost, compared to the large number of men they persuade to give up terrorism (and often become an informer.)
The U.S. Department of Defense has kept secret its data on the released terrorism suspects who returned to killing, because knowledge of who they know is back at it, would reveal what they know and how they came to know it. The American counter-terror officials are desperate to guard their secrets, since secrecy about what you know, and how you know it, is crucial in tracking down and catching terrorists. There is even less information released about the recruiting program. But this is an increasing subject of discussion of this on the Internet, and elsewhere, by Islamic terrorists and their supporters. Since 2009 those who have been arrested and released have come under increased suspicion. There appear to have been some executions of men who were not spies, although that has been going on for a long time. But now, just having been a prisoner of the Americans is enough to get you killed if you act in the wrong way, or say the wrong thing.