On 4 November 2001, San Francisco Chronicle staff writers Lance Williams and Erin McCormick reported that Ali Mohammad, an Al-Qaeda operative convicted in connection with the 1998 bombing of the U.S. embassy in Nairobi, Kenya, was a long-time FBI confidential informant:
http://www.sfgate.com/cgi-bin/article.cgi?file=/chronicle/archive/2001/11/04/MN117081.DTL
The FBI commonly uses polygraphy to vet confidential informants. Which raises the question, is Ali Mohammad yet another double-agent who beat the polygraph?