SCIENTISTS suspect that the gas pumped into the Moscow theatre was designed by Soviet military technicians during the Cold War. It would have been intended to penetrate nuclear bunkers and battlefield command centres, but has been refined since then for use in crowd control and sieges.

Soviet scientists were considered to be at the forefront of chemical and biological weapons design. After the Cold War, there were suspicions that Russian teams were still working secretly with toxins banned by international treaties.

The only official hint as to what was used came from one of the doctors treating the injured who said that it was some sort of “psychotropic” substance. Dr Yevgeni Yevdokimov, Moscow’s chief anaesthetist, said: “It is safe if used as a general anaesthetic, but large doses can affect basic functions of the organism, causing unconsciousness, respiratory and blood circulation problems.”

Dr David Scott, a consultant anaesthetist at the department of cardiothoracic surgery at the Edinburgh Royal Infirmary, said that anaesthesia was extremely delicate. “When conducted in a confined space like a theatre, you would always anticipate large numbers of casualties because the range of human reaction to any anaesthetic is very great. If, for example, 50 per cent of the people in the auditorium were put to sleep, you would expect another 40 per cent to be unaffected and 10 per cent to die.”

Dr Alex Colquhoun, consultant anaesthetist at the Royal Infirmary in Glasgow, said that since all the possible compounds that the Russians might have used would have been heavier than air, children — who were in the balcony — would have been less affected than those in the stalls.

The British doctors said that as the troops who stormed the building were not wearing biological warfare suits, the substance was unlikely to have been a virulent nerve gas such as sarin. Some American toxicologists thought it might have been a powerful sedative such as Valium or a form of BZ gas, a hallucinogenic drug first researched in the 1960s.

All that the specialists have to work on so far are the vague testimonies of the survivors. There was no obvious gas cloud, nor stinging in the eyes and throat associated with incapacitants such as CS gas. Some talked of a sour smell, like bitter almonds. It appears to have been colourless. Those nearest the ventilation shafts were worst-affected. Detailed blood tests will be needed to identify the gas.

A former colonel in the Russian special services, Yuri Bespalov, told the Moskovsky Komsomolets newspaper that it was likely to have been a largely odourless nerve gas that is supposed to paralyse people.

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