Putin is obviously going to blame Ukraine. I think Ukraine doing this is highly unlikely. They would not do this because it would be bad optics for Ukraine. (I know, speaking of optics with regard to such a travesty may seem callous, but wars are often callous.)
My next thought is this was a false flag attack by Putin so he could blame Ukraine or the US. The fact the US gave warning means that would not work against the US, but still could work against Ukraine. Reichstag fire anyone?
Another thought is this was Hamas or Hamas sympathizers who were upset Russia voted against the cease fire between Israel and Hamas in the UN.
Yet another thought is it was some anti-Putin faction in Russia. After all, a lot of powerful people including Putin supporters were likely to be at such an exclusive venue.
Again, definitely not the US. If it was us, why would we have tried to warn Putin?
Sure our intel services have a decent idea who did this, but Putin will probably again ignore any info we give Putin as propaganda.
Just spit balling here. Any thoughts about the above or other ideas?
Oh, should have added another thing pointing to false flag is a lot of anti-Putin people may have been there, and then Putin can blame Ukraine. Two birds with one stone. And he is that ruthless.
Again, definitely not the US. If it was us, why would we have tried to warn Putin?
Interesting thought but you forgot one thing, WHY WOULD THE US WARN PUTIN IN THE FIRST PLACE???
Why would Putin trust the US especially since our weapons are killing Russians?
This smells like a CIA setup. Find some pissed off people mad at Russia, give them drugs, money and guns and turn them loose.