1999, aimen dean embarks on a mission that might be his last returning to the al qaeda camps in afghanistan, no longer a jihadi but now a spy for british intelligence. i was talking a bus with one of my friends and i remember thinking about i m going to meet my comrades but this time not as a friend but i m going to see them as targets. reporter: his ability to live among former comrades and report on their activities would be rare and invaluable. you cannot replace human intelligence and the ability to get next to somebody when they are suspicious that you re trying to spy on them and they ll only talk to somebody they view as a friend. you can t replace it. reporter: and british intelligence would not be able to replace a secret agent like dean if he were caught.
i thought the only way i could survive is to basically suppress the spy in me and to basically let the jihadist in me be the dominant personality and to keep saying always i m a jihadist, i m a jihadist, damn the west, in order to basically make sure i do not slip, i do not make a mistake. reporter: dean knew any misstep could be fatal. if your cover is blown while you are there, no help is coming. afghanistan is a black hole as far as intelligence operations were concerned. it s just a place where you can t meet handlers, you can t transmit information. you are on your own. once you re going in, you re lost. once you re coming out, you re born again. if my cover is compromised, then i would have faced a tribunal and death. reporter: aimen dean did face death soon after his arrival in afghanist afghanistan, not at the hands of al qaeda but while fighting
smart neighborhoods running on a microgrid. a stadium powered with solar. a hospital that doesn t lose power. amazing. i like it. never gonna happen. reporter: august 7, 1998, truck bombs explode outside u.s. embassies in kenya and tanzania, killing 224 people, including 12 americans. this is the opening salvo of al qaeda s campaign of global terror. in afghanistan, al qaeda operative aimen dean learns of
whoever he fights and to make peace alongside them with whoever he makes peace with, to obey him in times of ease and in times of hardship, and that god is my witness. and that s it. reporter: osama bin laden was not yet the world s most wanted man. phil mudd is a former depp testify director of the cia counterterrorism center. i think there is someone in the intelligence community who knew al qaeda was slowly emerging but i don t remember people looking at him and saying this guy is going to become the center of the universe for the united states intelligence over the next five to ten years. no way. reporter: meanwhile al qaeda was working to develop weapons of mass destruction. aimen dean was assigned to work in its chemical weapons lab. they wanted to enable people, ordinary people, to purchase every day chemicals and to turn them into chemical weapons.
handlers. they were more or less shocked to hear it. they asked me to go over details, hours and hours describing every single second of that encounter. so they were guessing at the time that it will be an attack similar to the nairobi and tanzania in 1998 or again the u.s.s. cole in 2000. no one even guessed it s going to be on the magnitude of 9/11. there was a certain amount of chatter that something big might go down but the details of the plot were kept really quite secret. reporter: on september 11th, aimen dean was walking down a busy street in central london when he wait a minute upon a crowd. basically i saw lots of people congregating around a shop window, which was at the time one of the shops that sells big tvs and i looked at it and i saw one the towers of the world trade center on fire. and the first thing that came to my mind was this is al qaeda, no