Sims was last seen in Wichita Falls, Texas on the afternoon of December 9, 1961. He was alone with his older brother at their home in the 4600 block of Stanford when he went to go play outside sometime between 12:45 and 1:00 p.m. He has never been heard from again. His mother returned home at 2:30 p.m. and couldn't find Sims. The family searched for him without success before reporting his disappearance to police at 8:00 p.m.

Sims and his family had lived in Wichita Falls for only a short time prior to his disappearance. He and his brother lived with their mother and stepfather and had taken their stepfather's last name; their biological father lived with his second wife in California in 1961. Sims was a fifth-grade student at Jefferson Elementary School and was in the Boy Scouts. He apparently vanished without a trace; very little evidence is available as to his fate.