The gas entered the auditorium through the air conditioning system, put a fair percentage of those inside out of commission, and allowed Special Forces to successfully take control. The official story at first called the mission a total success. Ten hostages died in the crossfire, but everyone else made it, and authorities even managed to take the terrorists in alive. That story soon fell apart. The truth was that 50 terrorists had died (not too many tears were shed over them), and reporters saw hostages vomiting and choking as they entered the evacuation buses.
Authorities refused to identify the gas for doctors, so no one knew how to treat the patients. In the days after the siege, 120 hostages died from the effects of the gas. If you count everyone who died in the next year, the number rises to over twice that. Some of the survivors put together a lawsuit, so the closest thing this ordeal has to a conclusion is the European Court of Human Rights telling Russia to pay a couple million dollars to 64 plaintiffs. And as for Putin, his presidency ended in 2008, and of course no one ever heard from him again.