The Moscow theater attack had 850 hostages in a wide-open area, guarded by 40 CRI terrorists. The gas pumped into the building was also rather violent, some Fentanyl derivative IIRC. That's not even remotely comparable.
I think the intent here was to have the fentanyl put the assailants to sleep. Granted, it went horribly wrong. But violent isn't how I would describe the intent.
