Corrections Sgt. Tony Quinn says 48-year-old Marvin Lane Ussery was spotted late Wednesday night scaling the 7-foot tall, barbed wire-topped fence that encircles a large wooded area behind the California State Prison in Sacramento.
Quinn says Ussery served time at New Folsom for robbery before he was paroled in June 2009.
Officials are investigating whether Ussery was attempting to smuggle in drugs or cell phones, but say they haven't found any contraband.
Ussery is being held in Sacramento County Jail on suspicion of violating his parole and being an ex-convict on prison property.