Video: 'Facts About Moscow's 2002 Hostage Crisis At The Dubrovka Theater'

(Saturday, October 26, 2002, raid began at 5:20 a.m. Moscow Daylight Time; during the Moscow theater hostage crisis) — A four-day hostage siege by Chechen rebels at the crowded Dubrovka Theater in Moscow ended today with 131 of the 850 captives dead, most from a knockout gas used by Russian special forces who stormed the theater; all 40 rebels also died.

The attackers, led by Movsar Barayev, claimed allegiance to the Islamist separatist movement in Chechnya. They demanded the withdrawal of Russian forces from Chechnya and an end to the Second Chechen War.

Video: 'Situation Critical - S01E08 - Moscow Siege'

During the raid, Russian forces filled the theater with gas. Aleksandr Tskelo — a hostage and a producer of the musical Nor-Ost, which had been playing when the theater was seized on Wednesday evening, Oct. 23, 2002 — said the gas had put those inside asleep, but it was not clear what the substance was.

The identity of the gas was not disclosed at the time, although some believed it to have been a fentanyl derivative, such as carfentanil. A study published in 2012 concluded that it had been a mixture of carfentanil and remifentanyl.