The only reasonable conclusion is that the source -- or trail of sources -- is even more incriminating than the fake documents.
That is EXACTLY the reason why CBS won't reveal their sources. This tells me that the entire operation may have been pre-approved by high-level operatives in both the Democratic National Committee and Senator Kerry's campaign office with a willing accomplice in Dan Rather (who has a personal vendetta against the Bush family); once we find out the truth it will be pretty much "game, set and match" for the Kerry campaign.
The conspiracy to commit fraud must go higher than Dan Rather. The network exec could overrule Dan the Doyen at any time. And the Viacom owners could overrule the networks. They haven't. Why??