A key player in the Treasury Department's efforts to protect the nation's financial system from being abused by terrorists, drug dealers and other criminals is leaving.

William Fox, director of Treasury's Financial Crimes Enforcement Network, called FinCen, since December 2003, is taking a job with Bank of America as its senior compliance executive for financial crimes.

"Forging close bonds with both the financial and law enforcement communities, William worked to advance our vital interests in both national security and the free flow of capital," said Treasury Secretary John Snow.

Fox's last day at Treasury is Tuesday. He'll start work at Bank of America on Feb. 21.

FinCen's deputy director, William Baity, will serve as acting director after Fox departs.