In fact it seems have been a variant of nerve gas that the Russians used. Thats why they are not divulging what type of gas they used, despite Russian and international demands, with faamilies being denied information of their relatives.
http://www.telegraph.co.uk/news/main.jhtml?xml=/news/2002/10/28/wmosk28.xml&sSheet=/portal/2002/10/28/ixport.html
Rage at secrecy as gas kills 115 hostages
The gas used by Russian special forces to end the Moscow theatre siege killed 115 hostages, the capital’s leading doctor said yesterday. Only two were shot - a woman who was killed by the Chechen terrorists as she tried to escape last Wednesday and a man during the final battle. As the number of hostage deaths rose, the authorities refused to give details of the gas that was used. Andrei Seltsovksy, the city’s health chief, told a news conference that the 115 had died “from the effects of the gas exposure”. Yevgeny Yevdokimov, Moscow’s chief anaesthesiologist, said the gas was a “narcotic substance basically similar to a general anaesthetic in surgery”. But there was speculation that it could have been a form of nerve gas or defoliant. Michael Yardley, a London security consultant, said he thought it was BZ, an odourless incapacitant first used by America in Vietnam. About 800 people were being held in the Melnikova Street theatre by about 50 Chechen rebels demanding the end of the Russian occupation of their breakaway Muslim republic when the troops attacked before dawn on Saturday. Last night 646 people were still in hospital, including 150 in intensive care. The Russian media suggested that the number of deaths could double.
Western diplomats expressed anger that the Russians would give no details about the gas. They said also that the authorities had failed to tell them that the assault had been launched and, initially, which hospitals the survivors had been taken to. Later they refused to allow survivors well enough to travel to be flown home for treatment, saying that they were witnesses. An estimated 70 foreign nationals were held captive in the siege and at least four foreigners died. The three British hostages survived while almost all the 50 rebels died. Some embassy doctors did gain admission to Moscow hospitals to oversee the treatment of their nationals, but tempers quickly frayed when it became clear that nearly all the victims were suffering from gas poisoning. A diplomat said: “The embassy doctors were desperate to find out what kind of gas the Russians used, as you cannot treat someone properly unless you know what they have been poisoned with.” The United States embassy said it had asked for details of the gas - “but we have not received a reply as yet”. Russian doctors said that they too had been refused information about the gas.
Dr Seltsovsky said they were given only general information, but were not told the exact composition or name. The impact on the hostages had been more devastating than expected, he said. “In standard situations, the compound that was used does not act as aggressively. But it was used on people who were in an extreme situation for more than 50 hours. All of this naturally made the situation more difficult.” Some of the hospitals where the hostages were being treated closed their gates and refused admission to relatives yesterday. A woman in her forties told NTV television: "I am looking for my son - here is his photo. He is called Dmitry Rodionov. He was born in 1984. I cannot find him; he is on none of the lists. “If anyone knows him or those who sat close to him in the theatre - he is tall, sporty and dark-haired - please phone. I hope you can help.” Moscow’s main emergency hospital posted a list of names of the survivors on a door, while relatives swarmed around security guards at Moscow’s Hospital No 13, asking for information about loved ones.
Ekho Moskvy radio station said: “Former hostages have virtually found themselves under arrest.” President Vladimir Putin, whose reputation for decisiveness appears so far to have been strengthened by the swift end to the siege, described the Chechen fighters as “armed scum”. He said: “We proved that Russia cannot be brought to its knees.” But while he asked the relatives of the dead for forgiveness, the president offered no explanation about the gas. Mindful of a possible public backlash, the government announced that the families of those who died will each receive around £2,200 as compensation. The hostages who got out alive will receive half that amount. Moscow city council has said it will pay up to £300 towards the burial costs of each victim. Amid the relief on all sides that not all of the hostages had been killed, another urgent question was being asked: how did 50 heavily armed rebels, including 18 women, manage to enter such a closely policed city as Moscow without being detected?