From a letter to John Ellis:

If CBS were to acknowledge the documents to be a forgery, then they could not claim ethical responsibility to protect their sources. Once implicated, the sources might further implicate those who encouraged them. Where would this lead?

Has any reporter ever gone to jail for protecting the source of a forged document? A document which the reporter himself acknolwedges to be false?

CBS will continue to maintain authenticity. They have no alternative. They have been very clearly advised on this by their attorneys.

The risk calculations are much different than for an ordinary news fraud. The business cost to CBS of acknowledging forgery could ultimately be much larger than mere damage to the brand. Think Arthur Andersen.