No one in the whole movie ever asks anyone, Did you write this letter' Part of the reason is that no one wants to hear that it isn't for them. As soon as they read it, they want it to be theirs.
“I will be as harsh as truth, and uncompromising as justice... I am in earnest, I will not equivocate, I will not excuse, I will not retreat a single inch, and I will be heard.”