The man who once headed up the U.N. Oil-for-Food program is now the target of a criminal investigation by Manhattan District Attorney Robert M. Morgenthau (search).

Benon Sevan (search) is already under investigation by the Independent Inquiry Committee, a U.N.-approved special commission headed by Paul Volcker (search) that is investigating alleged Oil-for-Food corruption. The commission is looking into oil deals worth millions of dollars that Sevan allegedly arranged in exchange for kickbacks.

Sevan's name allegedly appears on documents relating to transactions with an oil company registered in Panama. Sevan repeatedly has told FOX News that he has done nothing wrong.

An interim Volcker report in February did not accuse Sevan of receiving bribes but did question how he ended up with $160,000 — money he claimed he received from a now-deceased aunt. She died after falling down an elevator shaft.

After the Volcker commission concluded that Sevan's management of Oil-for-Food was "ethically improper" and that it seriously undermined the integrity of the United Nations, Sevan was suspended.

Secretary-General Kofi Annan (search) has kept Sevan on staff with a $1-a-year salary as a way to ensure that as a U.N. employee, Sevan cooperates with the investigation. Although Sevan currently has diplomatic immunity, Annan has said the immunity would be lifted if charges are filed.

Annan said Tuesday he is worried how the latest development could hurt the United Nations but that he knew little about the case.

"I've been always worried about the damage to the organization and to all of us. But I don't want to get into the details. I have no details about the district attorney's proceedings," he said, adding that he was waiting for the Volcker committee to finish its work.

U.N. officials said that as far as they know, Sevan is cooperating with investigators, but they do not know where he is. Officials said they are looking into whether Sevan still has a diplomatic passport.

Volcker commission investigators haven't been in direct contact with Sevan recently. A spokesman told FOX News that the committee "currently handles Sevan's case through his lawyer. He remains a U.N. person shielded by diplomatic immunity ... there is no reason to think he is not in the USA."

Sevan did not return repeated phone calls seeking comment.

FOX News' Jonathan Wachtel contributed to this report.