THey (ALL the terrorists) worked with Anthrax/Biological weapons....without any protection. They weren't worrying about dying from it. The KNEW they were going to die from it....so that was enough incentive to go forward with the air attacks. Sort of like a ticking time bomb?
Become exposed the biological weapon...they have anywhere from 2-11 days to carry out the mission, and if they fail they die a terrible death from the anthrax..etc..
Consider how, in the future they could RECRUIT new terrorists this way....expose them and tell them to find a way to die within 48 hours or 'all-ahh' will be upset and the bug they have will be painful.
Hmmm..sounds like a movie script.