“Offered no evidence” is factually untrue
What’s the more plausible explanation - that a practically non-existent irrelevant-for-years terrorist group running unsophisticated operations in Syria suddenly assembled an A-Team to kill 150 people in Moscow, or that the Ukrainian citizen(s) who tried to flee to Ukraine committed the attack at the behest of Ukraine, which is currently at war with Russia? A real mystery!
In fairness, if Snowden was arrested while boarding a flight for Moscow that doesn't necessarily prove that Russia was behind his whistleblowing in some way.
I'm not saying that the Ukrainians didn't do this, just pointing out that this argument isn't solid by itself.