The Department of Homeland Security’s Inspector General, a federal watchdog group, released the report showing that DHS has major room for improvement in maintaining valid addresses for migrants to follow up with them.

“[Immigration and Customs Enforcement] must be able to locate migrants to enforce immigration laws, including to arrest or remove individuals who are considered potential threats to national security,” the report said.

“The notable percentage of missing, invalid for delivery, or duplicate addresses on file means DHS may not be able to locate migrants following their release into the United States,” it added. “As the Department continues to apprehend and release tens of thousands of migrants each month, valid post-release addresses are essential.”