In "The Departed", what did Leonardo's letter to Matt's girlfriend say?

Answer 1

The letter was evidence that was meant to be sent to Marky Mark, who honor Leo's death and kills Matt Damon. Leo's character knows that the courts and the police aren't enough to tackle the web of corportion.

Marky Mark ruled in that movie.

Answer 2

It told the truth about him, who he was and that he was an undercover agent . It also had info that Damon was dirty.