photo by: Richard Gwin

Linwood high school senior Randy Leach vanished from a graduation party in 1988. His parents, Harold and Alberta Leach, are pictured in November 2014.

Linwood ? A retired Kansas Bureau of Investigation special agent believes a teenage boy who disappeared 30 years ago after attending a party in rural northeastern Kansas likely drove off a bridge into a creek that swept the vehicle away, but he can’t prove his theory

Timothy Dennis investigated the disappearance of Randy Leach for more than a decade before retiring in 2010, The Kansas City Star reports.

“It’s the ones you don’t solve that haunt you,” Dennis said.

The 17-year-old Leach went missing in April 1988 after borrowing his mother’s car and attending a party near his home in the small town of Linwood. Witnesses told police that Randy was either drunk or high at the party.

At the time of his disappearance, theories abounded involving a drug overdose, dismemberment, the occult, and death by hanging — in a cave. Leach’s parents sued to see some of the investigative records, but a judge denied their request earlier this year.

Dennis believes the truth is less sinister. He suspects the teen drove the car off a single-lane bridge with no guardrails on its approach and tumbled into Stranger Creek. The bridge, which has since been demolished, was on a quiet back road. Dennis suspects Randy took that route because it was less likely to be patrolled by police.

Divers did find a vehicle in Stranger Creek, but it wasn’t Randy’s mother’s car. The dive team late found a different vehicle that had been pushed by the current past the massive pilings of a railway bridge. The discovery drastically dimmed Dennis’ hopes for the case.

“It went from a manageable search area to an unreasonable area,” Dennis said, “because if the current could push (a vehicle) this far, what’s to keep it from pushing it 100 feet, 100 yards, 100 miles?”

Stranger Creek feeds into the Kansas River, and the search extended there. But the river’s shallowness and sandiness deterred efforts.

Dennis said he closed almost all of the approximately 75 homicide or death cases assigned to him in his 24-year career, and he feels he did everything he could to achieve a breakthrough in the Randy Leach case.

“I prided myself with having a reputation of closing cases, and I thought I could close this one, but I couldn’t,” he said. “In my heart of hearts I think this is it, but I can’t prove it.”