TILLERY — North Carolina authorities said a 51-year-old man serving life sentences for murder and robbery has escaped while working on a prison farm.

The N.C. Department of Public Safety said in a release that James Ladd left his prison job Sunday outside Tillery prison in Halifax County. Ladd was operating a tractor on the farm. Officers found it abandoned just before noon. Tillery is a minimum security prison.

Ladd was convicted in 1981 for the shooting deaths of two men on a Yadkin County farm.

It's unclear why Ladd was housed at the minimum security prison. An agency spokesman could not immediately be reached.

According to the agency's Web site, Ladd's had seven infractions since 1981, most recently in 2010 for tobacco use. Prior to that, he disobeyed orders in 1992.