The investigation was being conducted by the Integrity Committee of the President's Council on Integrity and Efficiency, a group charged with investigating misconduct by agency inspectors general or their staffs, according to the Washington Post.
Most of the complaints came from current and former employees of Cobb's office. The complaints alleged that he suppressed investigations within the National Aeronautics and Space Administration and penalized his own investigators when they pursued cases, the Post said.
"We sent information from probably more than a dozen current or former employees to the integrity council," a spokesman for Sen. Bill Nelson, Dan McLaughlin, said in a telephone interview. "Senator Nelson received a letter from the integrity council notifying him that they would be conducting an investigation."
McLaughlin would not disclose the nature of the allegations made by the current or former employees. Nelson, a Florida Democrat who as a congressman once flew on the space shuttle, is the ranking minority member on the Senate Commerce subcommittee that oversees NASA.
The Post said at least 16 people provided documents and written complaints about Cobb to council, including that he hampered investigations into problems such as a malfunctioning self-destruct procedure during a space shuttle launch and the theft of data on rocket engines.
Cobb would not discuss the case with the Post but said, "The office has been particularly dedicated to ensuring an atmosphere where safety concerns are fully addressed."
In April 2005, The Daily Press of Newport News, Virginia, reported on allegations that Cobb had retaliated against NASA research pilot Robert Rivers in a dispute over aircraft safety.
Dan Samoviski, who retired in 2004 as deputy IG director for audits at NASA headquarters, told the Post, "Personally, I just think he created a hostile work environment."
Several sources also told the Post that Cobb suppressed audits and stopped investigations to avoid embarrassing NASA or its leadership.
Chris Swecker, assistant director of the FBI's criminal investigative division, leads the Integrity Committee. It also includes the head of the Office of Special Counsel, the director of the Office of Government Ethics and several sitting inspectors general.
Cobb was appointed by President Bush in 2002, after working for a year as an ethics lawyer in the office of the White House General Counsel. Of the 11 inspectors general appointed by Mr. Bush, nine had no previous audit experience.
"I am proud of, stand behind and am accountable for the work of the IG," he told the Post. "The office has been particularly dedicated to ensuring an atmosphere where safety concerns are fully addressed."
In e-mail, he urged his staff to "cooperate fully" with investigators.