WASHINGTON - 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 yesterday that Terry Vermillion was resigning. "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 about $200,000 per year.

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 unit, specifically its focus on drug-abuse cases instead of broader misconduct by large companies.

In September, Sen. Charles Grassley, R-Iowa, brought to light additional complaints against Vermillion in a letter to the GAO. Grassley said that an anonymous FDA whistle-blower contacted his office complaining that the GAO's most recent findings were "less than stellar" and did not include a number of questionable practices by Vermillion.

The whistle-blower alleged that Vermillion directed that reports "be changed to sanitize them of derogatory information" about former Secret Service colleagues working at the FDA.

Additionally, the whistle-blower said Vermillion used support staff to perform personal tasks for him and often directed department operations from his home in Hampton, Va.

Calls to Vermillion's office and e-mails seeking comment were not returned yesterday.