2002: Chechen terrorists seize the House of Culture theater in Moscow and take approximately 850 theater-goers hostage. The terrorists demanded the withdrawal of Russian forces from Chechnya and an end to the Second Chechen War. After a two-and-a-half day siege, Russian Spetsnaz forces pumped an unknown chemical agent (thought to be fentanyl, or 3-methylfentanyl), into the building's ventilation system and raided it. In the resulting fray, 39 of the attackers were killed by Russian forces, along with at least 129 of the hostages. All but a few of the hostages who died during the siege were killed by the toxic substance pumped into the theater to subdue the militants, causing a backlash against the government, especially for refusing to reveal the type of gas used in the assault.