The photograph shows a freed Russian prisoner pointing an identifying and accusing finger at a Nazi guard who was particularly cruel to prisoners at the Buchenwald camp. There is something really fascinating about this picture. That's all we can see of the prisoner's gesture here, but that finger means a lot.
Days, perhaps even hours earlier, that prisoner was too afraid to cross paths or even make eye contact with this man. Now he is putting an accusatory finger pointing a gun at the back of the man's head, and the defeated look on his face is acutely aware of this.
That medal on the guard's chest resembles a World War I Imperial Wound Badge, meaning that this guard fought for the German Imperial Army during the Great War. The badge is the black version (representing the third square, iron) and was given once or twice to people injured by hostile action (including air raids), or frostbite in the line of duty.