An African warlord's militia might be doing that most of the time in most places. I'm saying this is a shitshow of irregular quality, where it probably didn't happen in plenty of places, but it did happen in some, because the soldiers are angry, mistreated, and fed propaganda against the people they're occupying; and what discipline exists is more aimed at keeping them together and going in the direction they're supposed (in this case, stay put and occupy the town) to than it is aimed at keeping them from indulging their worst urges. They can't punch up so they punch down.
Again, for the reports to be true this doesn't have to happen everywhere, it just has to happen somewhere. Why is it so hard for you to accept that it happened even in one place? That a Russian soldier would shoot someone he's been told is a Nazi, and then ask himself, "Why stop at one?"
Did you see the video captured of the armored unit firing on a bicyclist during the time of Russian control?—exactly where they found one of the bodies, next to a bicycle.