A federal judge is ordering the IRS to explain under oath how it lost a trove of emails to and from a central figure in the agency’s tea party controversy.

U.S. District Judge Emmet G. Sullivan gave the tax agency a month to submit the explanation in writing. Sullivan issued the order Thursday as part of a freedom of information lawsuit by Judicial Watch, a conservative watchdog group.

The IRS says it lost the emails in 2011 when Lois Lerner’s computer crashed. At the time, Lerner headed the IRS division that processes applications for tax-exempt status. She has since retired.

Lerner has since become a central figure in several congressional investigations over the handling of tea party applications.

IRS Commissioner John Koskinen has already testified on the issue before Congress.

(AP)