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The head of the Food and Drug Administration's criminal investigation unit is stepping down, months after the latest round of criticism directed at his department by congressional investigators.

An agency spokeswoman confirmed Tuesday that Terry Vermillion told FDA staff this week that he would step down.

"We appreciate Terry's years of public service and wish him well in retirement," said FDA Associate Commissioner Beth Martino. Vermillion, who spent 20 years in the Secret Service before joining the FDA in 1992, is among the highest paid officials at the agency at roughly $200,000 per year. His department has been the subject of several investigations requested by federal lawmakers.

Earlier this year the Government Accountability Office said that the FDA must exercise more oversight over Vermillion's unit, which has operated largely independent of agency leadership, despite growing into a $41 million operation with 230 staffers over the last decade. In 2008, House and Senate Republicans questioned the priorities of the criminal investigations unit, specifically its focus on drug abuse cases instead of broader misconduct by large companies.

"I hope that with new leadership, this office will contribute more to the FDA's overall mission of protecting public safety," said Sen. Charles Grassley, R-Iowa, in a statement Tuesday evening. Grassley requested the GAO investigation of FDA's criminal investigation unit.

In September, Grassley brought to light additional complaints against Vermillion in a letter to the GAO.

Grassley said that an anonymous FDA whistleblower contacted his office complaining that the GAO's findings were "less than stellar" and did not include a number of questionable practices by Vermillion.

The whistleblower alleged that Vermillion directed that reports "be changed to sanitize them of derogatory information" about former colleagues from the Secret Service now working at the FDA. Additionally, the whistleblower said Vermillion used support staff to perform personal tasks for him and often directed department operations from his home in Hampton, Va.

Multiple calls placed to Vermillion's office and e-mails seeking comment were not returned Tuesday evening.

The FDA's Office of Criminal Investigations probes cases involving product tampering, counterfeit drugs, illegal marketing and other criminal activities that fall under the FDA oversight.

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AP Writer Mary Clare Jalonick contributed to this story.

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