Couple of points. It was not a gas. It was a powerful narcotic used in medicine as an anesthesia delivered in an aerosol form to increase the rapid reaction in order to incapacitate the terrorist. Robal2pl is dead on when he said It was the medical personnel. By not having enough medication on hand to bring them back once they had been put under. If the medical personnel had done this it would have ended up as one of the best mass HRT's ever done.

Below is a link that discusses this operation along with others of this kind.

"Offensive use of chemical technologies by US Special Operations in GWOT"

http://www.au.af.mil/au/aul/aupress/.../Text/mp37.pdf