The package contained a letter that said, "I know that you do some terrible terrible things and I can prove that you do these terrible things ... and sure enough what was contained in the package was proof that I do terrible, terrible things," Letterman told his audience.
The late night comic explained on air how his attorney contacted New York prosecutors to catch Halderman. Letterman later testified before a grand jury.
Halderman initially claimed that he was only trying to sell Letterman a screenplay, which included sordid details of the talk show host's life.
Halderman allegedly threatened to reveal "personal and private information" if Letterman did not accede to his demands to purchase the one-page screenplay, the Manhattan district attorney's office said at the time.
In October District Attorney Robert Morgenthau said the screenplay described a scenario in which Letterman's world would "collapse all around him" and would lead to a "ruined reputation."
ABC News' Sarah Netter contributed to this report