PORTLAND, Ore. (AP) - A Portland lawyer has told the Oregon State Bar that attorney-client privilege prevents him from discussing an elusive businessman linked to a CIA plane reported to have flown terrorism suspects abroad for interrogation.

An Oregon company registered to a Leonard T. Bayard - Bayard Foreign Marketing LLC - had owned a jet that reportedly was used in the CIA's "extraordinary rendition" program.

Scott Caplan has been the attorney for the Bayard company.

But news organizations and human rights groups looking into the rendition program have been unable to turn up evidence that Bayard is a real person.

The Oregon bar is investigating a complaint by Michael Munk, a former Rutgers professor who now lives in Portland, that Caplan is representing a person who doesn't really exist.

Responding to a letter from the state Bar, Caplan said he can't discuss Bayard because of attorney-client privilege.

"The ethical duty to maintain client confidences must be preserved even when disclosure would benefit the attorney," he wrote in a Jan. 31 letter to the Bar's disciplinary counsel, Mary Cooper, that was made available to The Associated Press.

Earlier in January, Cooper wrote him that not all attorney-client relationships are privileged.

"Under common law, absent peculiar circumstances, the attorney-client privilege does not shield the identities of clients," she wrote.

Cooper wrote that if Caplan knowingly registered a corporation under a false name he could face sanctions for professional misconduct.

But in his response to Cooper, Caplan insisted he followed the law.

Caplan said that without divulging client confidences, he could say "unequivocally" that prior to filing the articles of organization when he registered the Bayard company in Oregon in 2003, he knew of nothing to indicate it was not a legitimate legal entity.

He said he provided the company no services beyond filing the articles and learned of the company's acquisition of the plane 15 months later through press reports. He said he played no role in the purchase.

Caplan asked the Oregon Bar to find "there has been no wrongdoing" and end the investigation.

Munk said he recently saw the Gulfstream V jet for sale on a Web site listing by a Virginia aircraft broker, but the listing has been removed.

He said Amnesty International has determined it has changed hands several times since Bayard Foreign Marketing sold it.

Some suspects transported by the CIA rendition program have alleged they were tortured in the countries where they were sent. But U.S. officials have denied those claims.

(Copyright 2007 by The Associated Press. All Rights Reserved.)