Did American University professor James Thurber ever sign on to act as an independent ethics adviser for astroturf lobbyist Jack Bonner, in the wake of the scandal over those forged letters to lawmakers on climate change? The two principals can't seem to agree.

Thurber has now backed out of the gig, after an ad he ran in Roll Call praising Bonner raised questions about how independent he could truly be. But how firm was the arrangement in the first place?

Bonner told Congress late last month that he had "retained an independent ethics adviser who is well- regarded as maintaining the highest standards and independence," and that Thurber "has agreed to serve in this capacity."

But in a statement released through American University, Thurber said: "There was no contractual arrangement for me to be involved with Bonner and Associates pro bono or otherwise." He added that he had merely "mentioned to Mr. Bonner his need for ethics training for his staff."

A Bonner spokesman stood by Bonner's testimony, telling TPMmuckraker: "Professor Thurber told us that he would provide ethics training without fee, and he has now told us that he has decided he will not do that."

And on Thursday, Roll Call reported:

Thurber offered to provide pro-bono ethics advice to Bonner's staff, which he hasn't yet conducted. With the fallout from this week's ad, Thurber said he now won't provide that advice, and will recommend another ethics adviser to Bonner's firm. "I think its best not to do it."

It's a crime to lie to Congress. The Select Committee on Energy and Global Warming has said it is reviewing -- for possible referral to the Justice Department -- apparently false statements made by Steve Miller, the CEO of the coal-industry group on whose behalf Bonner 's firm forged the letters, during Miller's testimony on the episode.

Asked whether the committee might similarly review Bonner's claim to have retained Thurber, a spokesman for the panel declined to comment.