In 1940 AFAIK it was not known what Germany was going to do. Germany had concentration camps since 1933, but not yet extermination camps.

Yes, we do know what happened in Bucha. Quite a few people were killed by artillery. Then the worse elements of the Ukrainian army went in and executed anyone wearing a white armband (Russian sympathizer) or taking supplies from the Russians (blue food packs). The worst of the worst of the Ukrainian forces even posted videos of themselves executing prisoners.

I have no illusions that the Russians are guiltless in their invasion. Sadly, a near dicatator (Putin) is IMO the least worst of the three main actors in Ukraine.