who abused power and how did they do it

I might consider Lieutenant Kotler, one of the Nazi soldiers stationed at Out-With. He has "very blonde hair, an almost unnatural shade of yellow" (18). Gretl develops a crush on him, and it is implied that he is carrying on an affair with Mother. He is cruel and Bruno doesn't like him. He likes to abuse anyone that he feels is weaker than him. He doesn't care if they are German or Jewish. He is especially cruel to Pavel, an old man who prepares meals and waits on Bruno's family at Out-With.