A Senate subcommittee is investigating allegations against a top federal auditor accused of nepotism, abuse of power and cover-ups.

In a letter last week, Sens. Claire McCaskill (D-Mo.) and Ron Johnson (R-Wisc.), the chairman and ranking member of the Financial and Contracting Oversight subcommittee, asked Homeland Security deputy inspector general Charles Edwards to cooperate with the panel’s probe.

All told, the subcommittee is investigating nine claims against the auditor. Among them, Edwards allegedly employed his wife, Madhuri Edwards, as a supervisory auditor within his office, apparently violating laws and regulations governing personnel practices, the letter said.

When staff called attention to the matter, the auditor threatened retaliatory action, according to the letter.

Edwards also allegedly changed and withheld “relevant and damaging information” from an investigation into the Secret Service scandal involving prostitutes in Columbia. Former Secret Service director Mark Sullivan apologized last year for what he described as “misconduct” by his agents.

Whistleblowers have additionally accused Edwards of asking employees to do his homework and write his Ph.D dissertation, and they say he used office funds to attend classes in Florida, the letter said.

The senators have asked Edwards to provide documents and communications relating to the allegations by July 19.

“I am very disturbed that false allegations have been made against me, but more importantly, I am very concerned that this matter may negatively impact the important oversight work of the Office of Inspector General,” Edwards said in a statement Tuesday. “I will defend myself against these personal attacks.”

Edwards added that some of the allegations in the subcommittee’s letter were already reviewed and dismissed by other oversight bodies, including the Council on Inspectors General on Integrity and Efficiency.

Edwards became acting inspector general for Homeland Security in February 2011, and he has served as deputy inspector general for the agency since January.

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