WICHITA, Kan. (AP) — A registered Kansas sex offender has pleaded guilty to one count of sending obscene material to a minor while he was a patient at Larned State Hospital.

The U.S. Attorney’s office announced Monday that 34-year-old Christopher M. Case pleaded guilty to transferring the material. Case was a resident of the state’s sexual predator treatment program at Larned when the crime was committed.

Prosecutors say Case used a cell phone to send an obscene video to a 13-year-old girl in Montana.

Case is expected to be sentenced to 20 years in federal prison.