Dennis was visiting the Great Smoky Mountains National Park with his father, his grandfather, his older brother and two cousins on June 14, 1969. The family lived in Knoxville, Tennessee at the time. Dennis was last seen between 2:00 and 4:00 p.m. that day as he played a game of "Hide and Seek" in Spence Field in the park, near the Appalachian Trail. He disappeared behind a bush in the area and has never been seen again. An extensive search of the area did not locate any evidence as to his whereabouts.

Dennis was a special education student at the time of his disappearance. He is described as a "husky, healthy" boy who had hiking and camping experience and wasn't particularly fearful. His case remains unsolved.