Manhattan DA used sting to stop Letterman plot

** FILE ** In this image originally provided by CBS, David Letterman appears on the "Late Show with David Letterman," in this Oct. 8, 2007, file photo, in New York. Letterman acknowledged on his Thursday Oct. 1, 2009 show that he had sexual relationships with female employees and that someone tried to extort $2 million from him over the affairs. CBS says an employee has been charged with attempted grand larceny in the case. (AP Photo/John Paul Filo, CBS, File) ** MANDATORY CREDIT; NO SALES; NO ARCHIVE; NORTH AMERICA USE ONLY **