The Russians gassed the hall, killing many people.
There were three significant terrorist attacks in Russia around the early to mid 2000s decade, two in Moscow (an apartment building and a concert hall) and one in the Caucasus region (the Ruslan school siege). All three of them ended with armed interventions and talk about Russian FSB involvement, or incompetence. So you have to wonder what actually happened in this case.
If Putin blames Ukraine and the usual suspects start talking about a massive reprisal, it would just increase suspicion of a planned event, or one allowed to proceed despite intel.
But I don’t claim to know. I don’t trust any governments at this point, except maybe Hungary and Argentina. (Alberta possibly)
Didn’t they use a derivative of fentanyl?