Question about the ending (spoilers, obviously)

So at the very end... who killed Suzie? Was it a German soldier? I felt a bit lost at the end, I expected to see some indication of whether Malek ever stopped fighting tooth and nail against growing up and where his obsessive fetishism of war led him. The final scene is 6 years later, so he would be 18 or 19... at first I thought it was he who was playing the piano, but there seemed to be no cues at all whether it was him or not. If it was him, that is a very fitting ending... but why no indication whatsoever of it being him? Was it just a random German soldier?