LINWOOD, Kan. (AP) — A retired Kansas Bureau of Investigation special agent says he believes a teenager who disappeared nearly 30 years ago died after driving into a creek.

Timothy Dennis spent more than a decade investigating the disappearance of Randy Leach. The 17-year-old went missing in April 1988 after borrowing his mother’s car and attending a party near his home in the town of Linwood.

His parents have sued to see some of the investigative records in the case, but a judge denied their request. Dennis, speaking publicly about the case for the first time, says the most reasonable explanation is that the teen’s car went off a single-lane bridge. The creek was searched, but Dennis fears the car was swept too far downstream to be found.