Was the gas legal?

The gas had tragic consequences

By Jonathan Marcus BBC defence correspondent

There is still considerable uncertainty surrounding the identity of the gas used by Russian security forces in their storming of the theatre in Moscow.

Stipulations of the Chemical Weapons Convention

Never use chemical weapons

Never develop, produce, stockpile or retain chemical weapons

Never transfer chemical weapons to another party

Undertake to destroy all chemical weapons and production facilities

Undertake not to use riot control agents as a method of warfare

Some independent experts have likened its effect to that of an incapacitating substance known as BZ - a type of chemical weapon that figured in both the Russian and US Cold War arsenals.

By using what turned out to be a deadly chemical to end the hostage crisis, Russia's armed forces may well be guilty of a terrible misjudgement.

Whatever the gas was, it killed more than 100 people, and questions are now being asked about Russia's compliance with the Chemical Weapons Convention, which bans the use of such weapons.

Weapons treaty

Using such a gas in a confined space against a cross-section of society - young people, the elderly and many with pre-existing medical conditions - was always going to have unpredictable results.

In fairness, the dangers had to be set against the possibility that the hostage-takers would carry out their threat to kill hundreds - an agonising calculation for the Russian authorities.

But there are those in the West who wonder about the chemical used.

Hundreds of hostages are still in hospital

Is this something that the Russians have been developing in breach of the Chemical Weapons Convention that bans the manufacture, stockpiling and use of such arms?

The extraordinary secrecy surrounding the identity of the gas has only compounded the problem.

Experts acknowledge that there are grey areas in the treaty.

The convention was intended to abolish chemical weapons once and for all. But it continues to allow the use of very mild agents - like CS gas for example - for riot control purposes.

Both the Russian and US armed forces have continued research on a range of so-called non-lethal or incapacitating agents.

The idea is to find ways of defeating an enemy - say in a heavily built-up area - without causing huge numbers of civilian casualties.

But this sort of research pushes against the boundaries of the Chemical Weapons Convention.

As the tragic Moscow example shows, the context in which a gas is used can profoundly influence its effects.