For the love of GOD, they helped each other invade Poland! EVERYONE knows this. I'm perfectly aware of all the Nazi atrocities, and I'm also aware that the Peace, Land and Bread slogan was completely abandoned during Stalin's time. Lenin wanted those things for the Soviet people. Stalin wanted those for himself and his closest yes-men. If calling me a Nazi is the only argument you can get on your side and you are supposed to be some kind of revolutionary vanguard, this revolution is fucked.
The reason they used German weapons for the massacre was that they caused less recoil and so they could be more reliable for a one-shot kill. Also, they got them because the Soviets and Nazis were working closely together at the time. LIKE I'VE BEEN SAYING THE ENTIRE TIME.