A new report critical of United Nations oversight investigators raises questions about the organization's ability to investigate wrongdoing and Secretary General Kofi Annan's willingness to do so.

The report released this week details an independent probe conducted by Washington lawyers Jerome Ackerman and John Vanderstar into charges that that former Undersecretary General Dileep Nair was promoting favorites in violation of U.N. rules and possibly doing so in return for money and sex while serving as head of the Office of Internal Oversight Services.

Annan, who commissioned the report over a year ago, ordered the the case closed because the investigation found no evidence Nair received money or sex in exchange for promotions and even wrote Nair a personal letter expressing "personal dismay" for suffering "unnecessary and unmerited public innuendo."

But Annan's response did not address the thrust of the report: revelations that Nair violated U.N. promotion rules exactly as charged. Moreover, Annan made no mention of the report's details on how personnel at the Office of Internal Oversight (OIOS) stonewalled investigators by failing to provide requested computer records and internal documents, including a document request made three months ago. As the report itself discloses, Annan had personally ordered all U.N. personnel to cooperate in providing such information.

"To date, neither a response from OIOS to the March 2006 request nor any further OIOS documents have been provided," said the report. "(OIOS) also limited our interviews of individuals who might have provided relevant information."

Nair, who has since moved on to a job with the Malaysian government, refused to make himself available to investigators but dismissed the probe through his lawyers as a "witch hunt."

Ackerman, who led the investigation, expressed surprise at the low level of cooperation given by members of the office charged with enforcing U.N. regulations.

"We did not get what we thought we would get," he told FOX News.