Hydrogen cyanide gas: 'low-end' terrorism / JANE'S TERRORISM & SECURITY MONITOR, 6 Jul 2006

http://digbig.com/4mbpk
"The Al-Qaeda leadership called off a hydrogen cyanide gas attack on the New York subway system in 2003, according to a recently published book that estimated the attack would have resulted in 3,000 casualties. This estimate is probably over-exaggerated. Jane's has reviewed a jihadist manual for the construction of a mubtakkar gas device similar to the one described and found it lacking in detail and unlikely to be an effective weapon. While it may never be known why Al-Qaeda called off the attack, it is possible that the leadership were aware of the limitations of the weapon and preferred to wait until a more effective chemical weapon had been developed or acquired." [Sub Required]