Even if the Grand Duke could not be swayed by testimony, surely he would not ignore evidence such as that! Waller expected that he would have to explain the theory of fingerprinting before the full import of the evidence would be understood, but surely the Grand Duke would soon see that justice had not been served by executing Herr Fenster!
And this is how you break a boy: tell him he is king. Simple, but not easy. You must watch him, hawk-like, to see how he slips beneath your lies. You must seem to believe it enough that the boy believes, too. You must crown him and put him at the front of an army. If you fail, there is always another handsome hazel-eyed boy somewhere in the world. Anyone might do.