Stillwater prison warden Steven Hammer has been placed on leave pending a Department of Corrections investigation.

Prison officials aren’t releasing any details regarding the nature of the probe, but department spokeswoman Sarah Fitzgerald confirmed Hammer has been on leave since Monday. He is still on the payroll.

Hammer worked previously as warden of Rush City prison, and took over the top position at Minnesota Correctional Facility-Stillwater — the state’s second-largest prison — in March 2015.