The Osage County sheriff said he is "100% certain" Dennis Rader was involved in the 1976 disappearance of an Oklahoma girl.On Tuesday, Oklahoma deputies searched the former property of the BTK serial killer in Park City, Kansas. Rader referred to himself as BTK-bind, torture, kill. Osage County authorities told ABC affiliate KAKE they received a tip about the 1976 disappearance of Cynthia Kinney. KOCO's Tulsa partner reported the sheriff interviewed Rader back in February, searching for new leads.| MORE | Oklahoma officials investigate convicted serial killer's former property in Kansas Kinney was last seen on June 23, 1976, in Pawhuska. According to the National Missing and Unidentified Persons System, Kinney was last seen leaving the Osage Laundromat and getting into a 1965 faded beige Plymouth with two women.Osage County Sheriff Eddie Virden told ABC affiliate KAKE that during Tuesday's search, officials found items buried deep in the ground. Officials also found some items during a previous search of the property in April, including a piece of pantyhose that was ripped and aged.On Wednesday, Virden told KAKE he's 100% certain Raer was involved in the disappearance of Kinney.According to ABC News, another case being investigated is the death of 22-year-old Shawna Beth Garber, whose body was discovered in December 1990 in McDonald County, Missouri. The autopsy revealed she had been raped, strangled and restrained with different bindings about two months before her body was found.Garber's remains weren't identified until 2021.Top HeadlinesDeer Creek man arrested, accused of sexually assaulting underage girlsSon pilots United Airlines flight with mom on board as a flight attendantFrustrations run high after OKC venue closes despite customers having bookingsOklahoma officials investigate convicted serial killer's former property in Kansas