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 know dozens of these agents. Two of the most prominent double agents cane from Guantanamo. Abdul Rahman, an Afghan, who was released, returned to terrorism in Pakistan and found out and killed. The another, a Saudi Arabian, was released in 2007, returned to Saudi Arabia, went through a mandatory rehabilitation course. There he was apparently recruited by Saudi intelligence. Once out of rehab, the man went to Yemen, joined the al Qaeda organization, and then got back to Saudi Arabia two months ago 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. But there are apparently a lot more (perhaps hundreds) more such agents out there, and some 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.
There are plenty of prospects. Every man (and some women) arrested as suspected terrorists are potential agents. There are over 500 men released from Guantanamo, along with nearly 100,000 arrested in Iraq, Afghanistan and elsewhere. For example, last year, the U.S. released over 5,000 suspected terrorists it was holding in Iraq. Since then, dozens of them have been killed carrying out terror attacks, or arrested by Iraqi police for being part of terrorist groups. Iraqi and American counter-terrorism warned that a wholesale release of American held terror suspects would get people killed. But letting all those guys (they were mostly guys, and mostly Sunni Arabs) go was the politically correct thing to do, and off they went. Several hundred Iraqis, and a few Americans, at least, have died as a result. So far. But there were also apparently some agents recruited from among those released, not just last year, but in previous years as well.
It may never be known exactly how many of the released suspects returned to their murderous ways, or agreed to spy for the Americans. All of them were held because there was some evidence of involvement in terrorist activity. But the Iraqi police would not accept all the American evidence or, in many cases, did not consider it sufficient for an Iraqi arrest warrant. All this was driven by the desire to empty the U.S. prisons, without overwhelming the Iraqi justice system. Mission accomplished. However, as long as these men were in custody, recruiting attempts went forward. Many potential spies were willing to work with the Americans, but not the Iraqi government. The Americans were considered more reliable, and could get you out of Iraq (perhaps even to America) if you delivered.
Guantanamo, on the other hand, is a more difficult place for recruiting. Over ten percent of the 534 terrorism suspects released from Guantanamo had returned to Islamic radical activities. 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 14 of the 117 Saudis released from Guantanamo Bay, have 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 (and 11 are still on the loose) 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. Over the last year, 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.