Barnett was visiting his paternal grandparents' home on August 31, 1982. They lived on Hillcrest Farms, a chicken farm in the Grangeville, Idaho area. The farm was seven miles north of Grangeville and encompassed several hundred acres. Barnett was last seen sitting in a wagon in front of one of the barns while dozens of workers were unloading a delivery. He has never been heard from again. His family started searching for him only fifteen minutes later, but no one found any clues as to his whereabouts. Bloodhounds tracked his scent to a fence line on the northwest part of the farm, then lost the trail.

Barnett's grandparents were suspects in his disappearance for almost two decades afterward. His grandmother reportedly acted oddly, and she took a polygraph and failed. She took another polygraph exam in May 2001, however, and was cleared of an involvement in Barnett's case. Barnett's grandfather also agreed to take a polygraph, but he died before the exam could take place. Barnett's parents live in Oregon and his mother has been active in the search for him. His disappearance remains unsolved.