According to the warrant, the suspect, "48 Hours" producer Robert "Joe" Halderman, sent Letterman a package which allegedly included treatments for a screenplay with supporting materials.
The warrant goes on to say the "supporting materials" included copies of parts of a diary and correspondence belonging to Birkitt.
Halderman allegedly sent more documents, including letters, emails and photos.
On September 23, Halderman allegedly told undercover cops he wouldn't make the diary public if Letterman anted up $2 million.
Letterman acknowledged on his show last night he had sexual relations with female members of his staff.
Birkett has been a regular on Letterman's show (see video).