In Moscow terrorists took a thousand people hostage and threatened to kill them. The Russians problem was how to get them out, alive.
A traditional type of assault under this circumstance was highly unlikely to be successful. The Russians needed another option and fortunately they had one.
When special forces stormed the building they used a secret weapon never tried before. A mysterious knockout gas put over a thousand people to sleep. A hundred and seventy never woke up. The Russian authorities claimed the gas was not lethal but they refused to say what it was.
