I cannot recall the name of the city, but I think I know what you’re referring to. About 25 years ago, there was some terror group in Russia that held an entire theater hall full of paid customers hostage. After several days of negotiations that went nowhere, a certain type of gas was piped into the theater ventilation system. I believe that resulted in several score people dead, including the four terrorists.
This may have been just after the end of the Cold War. No one ever speaks of it anymore. I do remember that sadly, many children also perished, their bodies later found sitting next to their parents. This was before the internet was widely known or used.
Actually I think it was a school.🤔