CBS decides that it doesn't want to risk affecting the election.
Whew, now that we got caught trying to affect the election with fraudulant documents we certainly wouldn't want to affect the election by publically admitting that our producer revealed a 'confidential' source to the Kerry campaign before the story ran. Wouldn't want to reveal how obvious forgeries from a well-known kook got passed off as real. That might affect the election.
Nope, affecting the election in a way that might be detrimental to Democrats is against the unofficial code of journalistic ethics.
It doesn't take months to figure out what went wrong with the hit job by Rather. It is a simple investigation. Did he rely on a source known to be unreliable? Yes. Did he say that the source was 'unimpeachable'? Yes. Were the documents forged? Yes. Did CBS have a good reason to believe they were genuine? No. Did CBS's experts warn them that the documents appeared to be fake? Yes. Did CBS claim the documents came for a personal file? Yes. Did they know any such thing? No. Did CBS tell the Kerry campaign about these documents before they aired? We don't know. Did Lockhart talk to Burkett about the documents? Of course, there was nothing else for them to talk about, but that will never be proven.
Shouldn't take much longer than a week or two to nail that down. CBS was able to rush unverified documents to prime time in about the same window. But they only want to affect the election if they can help Kerry. If their investigation won't help, it has to be delayed.