>>> it's the kind of thing we never know about while it's happening because we're not allowed to, but tonight we are learning more about a secret area at guantanamo bay called penny lane where after 9/11 the cia took a sizable risk. we get more on the story from our chief foreign affairs correspondent andrea mitchell .

>> reporter: hidden only a few hundred yards from the guantanamo prison 's administrative offices a top secret compound of cottages now abandoned, but ten years ago, following 9/11, code named penny lane . an ironic illusion to the beatles song just as gitmo was code named strawberry fields . in fact, what went on at penny lane was more like "homeland" than a magical mystery tour .

>> it's not a trial. it's a quick execution you're facing here. you'll be tortured first.

>> i'll tell you everything you want to know, chapter and verse, but i can't go back. no, i won't.

>> yes, you will.

>> no, i won't!

>> reporter: just as in the tv series the cia tried to turn hard core guantanamo detainees into double agents and infiltrate them back into al qaeda .

>> it would be irresponsible for the cia or other intelligence organizations not to use these means to help protect the united states against future attacks. and that might well include using these operatives as future agents to disrupt other attacks.

>> reporter: the prisoners were enticed with penny lane 's special accommodations. real beds and mattress, private kitchens and showers even pornography for those who asked and they were paid millions from a secret account code named pledge. but there was the threat when returned back home they'd turn into terrorists and attack the u.s.

>> i think it was a very ill conceived program for them to thing that because these are some very hard core individuals and many of whom have been released by both administrations have gotten back in to fight us and our allies, unfortunately.

>> reporter: former officials say the cia even considered sending some pakistani former guantanamo prisoners back to u.s. on student visas to help track down a u.s. terror cell. that idea was apparently dropped and there's no evidence that any of this ever worked. by 2006 the entire project was abandoned. penny lane remains. eight overgrown cottages a testament to the desperate mind-set after 9/11. andrea mitchell , nbc news, washington.