If you are talking about the thumbnail, then if I am not mistaken the smaller pipe is 30 mm auto cannon, larger is 100 mm cannon. Vehicle would be BMP 3.

If anything, there is one arm missing

While I may be inclined to agree that videos like these shouldn’t be shared I can’t help but to strongly disagree with the rest. Killing armed enemy combatants is not a murder. He has a rifle on his back and is clearly not surrendering. What do you propose that Ukrainians should do, let themselves and their families be killed because he was alone?

And no military gain from killing an invader? You must be joking, right? How else are they meant to defend themselves if not by taking out the enemy?

Realistically it wouldn’t be a good thing, Russia and pro russian idiots would blame Ukraine and it’s not like we’d get someone better in charge either.