What did/didn't it say?
To me it seemed he was dancing around someting which he didn´t say straight out. It is a long time since I read that letter, I wouldn´t know where to look for it.
As far as I remember, he did not say, stress, emphasize that he was innocent. The letter was in a comprehensive, soft tone, not angry as you would expect.
Nothing really palpable, just gave me pause for thought. And doubt.