Germans (including gestapo) gassed a few million people here. Soviets (including NKVD) liberated survivors.

But maybe I read wrong history books.

That wasn't what I meant, I'm confused why you're associating the Gestapo with Eastern Europe. They were active in all of German controlled Europe with a pretty bad reputation almost everywhere. The nazi mass murders also have more of an association with the SS rather than the Gestapo, especially when it got worse in the later years.

(FYI, the NKVD killed more than 100'000 Poles in a just a few months in 1941. I haven't found a total. But they were also active in all of the CCCP. Not sure what would be an Eastern Europe specific reference here…)