Gut feeling is that it's another Chechen attack, though.
Why that? Do you have personally any vital interest?
It's quite possible - Russian security has been so incredibly beefed up
Don't think so. They offer suport to catch the assasin and the ties with Belarous seem to me quite strong. Furthermore the Russian intelligence services seem to click quite well and they will not allow any kind of bs close to their borders, whatever the motivation of those distracters might be and from where the money keeps flowing.