Details of Disappearance
Sumner was last seen in Gerty, Oklahoma on April 24, 1978. He lived in Oklahoma City and left on a trip to the ranch in Gerty where he and his wife kept horses and cattle.
At 2:00 p.m., he saw a female friend at her home for a short time and told her, "This is the last time you will ever see me." Because Sumner had a reputation as a prankster, the woman didn't pay much attention to that statement. He has never been heard from again. His brown 1975 Ford F-150 pickup truck, and the two guns he carried in it, has never been recovered.
It's possible that he was a victim of Claude Eugene Dennis and Michael Charles Lancaster, who escaped from the Oklahoma State Penitentiary on April 23, the day before Sumner disappeared.
Lancaster had been serving a 25-year sentence for armed robbery and Dennis had been serving a 50-year sentence for killing three people when they escaped by tunnelling under a wall. They then went to a nearby house where a prison guard and his family lived, broke in, and stole food, guns and the family's yellow Datsun. They left in the Datsun, leaving the guard's family unharmed.
They didn't resurface for another five days, and when they did they killed a fisherman near Farmersville, Texas. Over the next month the two men went on a crime spree across three states (Oklahoma, Alabama and Texas) and killed eight people altogether, including three state troopers, before they were themselves killed in a shootout with police in Caddo, Oklahoma.
About a month after Dennis and Lancaster were killed, the guard's yellow Datsun they'd stolen on the day of their escape was found in a densely wooded area behind a barn in Gerty, Oklahoma, near Sumner's ranch.
Because of the circumstances, there's a theory that Dennis and Lancaster encountered Sumner, kidnapped him, stole his pickup truck and used it to travel to Texas where they killed the fisherman. It's possible that the escaped inmates were waiting outside in Sumner's pickup when he spoke to his friend, and that when Sumner told her she would never see him again, he was trying to communicate that he was under duress.
Other than the circumstances, however, there is nothing to connect the two men to Sumner's disappearance, and it's not the only theory in his case. Another line of inquiry police pursued was whether Sumner's disappearance could have been connected with a dispute with neighbors over a fence.
Sumner was declared legally dead in 2007. His case remains unsolved.