Halderman pleaded not guilty in a Manhattan court last week to a count of attempted first-degree grand larceny in the $2 million plot. Letterman divulged details of the alleged extortion caper during his show, including the admission that he had had affairs with women who worked for him on "Late Show."
Birkitt was an assistant to Letterman and frequently appeared on camera with the host in comedy bits. She has also worked at "48 Hours Mystery." Calls to her home and her parents' home in New Hampshire went unanswered; a message left at her father's dental office wasn't returned Monday.
She moved in August to Manhattan, to a second-floor apartment of an Upper West Side co-op building. Neighbors said they did not know her well, and never saw Letterman in the building.
"She seems like an enigma," said Iris Rutkoski. "Nobody seems to know her in the building."
Rutkoski said she might have said hello to Birkitt in passing, but "I wouldn't recognize her to fall over her. She was not the kind to chat with her neighbors."
Halderman apparently copied the pages before they broke up, using them together with other e-mails and information in a package left in Letterman's limousine that was intended to extort money from him, officials said.
Halderman's attorney, Gerald Shargel, said Monday the charge against his client is "so obviously out of character to the point of not making any sense." Shargel said that Letterman manipulates audiences for a living and that to think he "gave the entire story and there's nothing more to be said is simply wrong."
CBS said it had no comment.
Associated Press Writer Karen Matthews in New York and AP photographer Jim Cole in New Hampshire contributed to this report.