Source is Putin's speech trying to justify the invasion of Ukraine on Mar 16, 2022.
Ironically, Yevgeny Prigozhin dismissed this justification for russia's invasion, that Kyiv was planning an attack on Donbas and Crimea. Prigozhin called it a lie.
Ukraine war based on lies: Wagner mercenary chief
https://www.nbcnews.com/video/wagner-boss-prighozin-says-russian-military-chiefs-lie-to-putin-over-ukraine-war-184392773794
Even then, Prigozhin did not attack Putin directly, he said Putin had been lied to. We think of Russia as being a rigid, top down dictatorship, but, the leadership are almost all a bunch of gangsters who kill each other, Pooty being top gangster. I think there’s a good chance an insulted or threatened general ordered the hit. Then can claim it was a mistake, the work of subversives or more traitors, infiltrators (would be rather embarrassing), etc. I also think there’s a high likelihood we’ll never know the truth.
That said, how far into Russia can our AWACS see a S-300 launch?