I've had letters that contained confessions to crimes, expressed their anger with the police, threatened the judge, threatened me, and provided apologies to the victims.
My office has even received letters containing a defendant's bodily fluids. Thankfully, I haven't received one of those and the letters are screened first.
This is one of my favorites. Clear, concise, and to the point. Especially the part about not wanting to cost the taxpayers any more money.