The agency tasked with overseeing billions of dollars in U.S. aid to Afghanistan is undergoing more changes.

Herbert Richardson, the acting special inspector general for Afghan reconstruction, has announced he is resigning.

Richardson said he was leaving to pursue an opportunity in the private sector. He had been leading the agency known as SIGAR since January, when the previous special inspector general stepped down after being accused of mismanagement.

The U.S. Congress has appropriated over $70 billion since 2002 to improve security and development in Afghanistan. A recent audit by the U.S. special inspector general for Afghan reconstruction said the aid could be financing corruption or fueling the insurgency. The agency said the Afghan government had hampered efforts to track the assistance.

Richardson leaves next month.