If they ignored warnings from even relatively friendly states then I find it difficult to see the whole thing as something other than sacrificing some of their own people so they could wring some propaganda out of the event to shore up support for their war. When it first happened and they tried to lay the blame on Ukraine I figured it was more a case of, "Never let a serious crisis go to waste," but it really seems like they knew it was coming and allowed it to happen.
So everyone and their mother warned them beforehand, but they allegedly knew nothing. This has some 1999 Russian Apartment Bombings vibes. Not that it is any surprise anymore at this point, that Russia would sacrifice their own civilian population to push an agenda.
it's ridiculous to think that Russian security services knew nothing about this attack, so they obviously allowed it to happen at least.. because they were somehow right there ready to catch all of these guys, with no problems.. and they were ready to interview them and upload those interviews to the internet just minutes after the attack.. but they somehow didn't see it coming, even though the Iranians and the Americans both knew something was up..