Kolokol-1 is thought to be the chemical agent employed by a Russian Spetsnaz team during the Moscow theater hostage crisis in October 2002 . At least 129 hostages died during the ensuing raid ; nearly all of these fatalities were attributed to the effects of the aerosolised incapacitating agent that was pumped into the theatre to subdue the militants . The gas was later stated by Russian Health Minister Yuri Shevchenko to be based on fentanyl . Minister Shevchenko 's statement followed speculation that the gas employed at the theater violated international prohibitions on the manufacture and use of lethal chemical weapons , and came after a request for clarification about the gas from Rogelio Pfirter , director-general of the Organisation for the Prohibition of Chemical Weapons . The minister stressed that the drug fentanyl used in the gas , which is widely used as a pain medication , " can not in itself be called lethal "
Moscow theater hostage crisis
Moscow theater hostage crisis
Kolokol-1