MY DOUBTS ABOUT THE “SLEEPING GAS” appear to be correct:

The doctors in the footage described the gas as being a neuro-paralyzing agent, one that disables the body’s nervous system. The description contrasts with other reports that described it as a sleeping gas.

Several readers point out that it seems to have killed an awful lot of the terrorists in proportion to the hostages. I’m reminded of the “Vee-Two nerve gas” from E.E. Smith’s vintage science fiction stories: disabling, but fatal after a while without the antidote. This seems quite similar.

(Link via Shoutin’ Across the Pacific).