Authorities in Oklahoma and Missouri are investigating whether the BTK serial killer was responsible for other homicides, with their search leading them to dig this week near his former Kansas property in Park City.

Osage County, Oklahoma, Undersheriff Gary Upston told The Associated Press on Wednesday that the investigation into whether Dennis Rader was responsible for additional crimes started with the re-examination last year of the 1976 disappearance of Cynthia Kinney in Pawhuska. The case, which was investigated on and off over the years, was reopened in December.

Upston said the investigation “spiraled out from there” into other unsolved murders and missing persons cases.

“We sit just on the other side of the state line from Kansas and Wichita, which is his stomping grounds. And so yeah, we were following leads based off of our investigations and just unpacked other missing persons and murders, unsolved homicides that possibly point towards BTK,” he said.

Rader, a city code inspector in Kansas, was arrested in February 2005 — a year after resuming communications with police and the media after going silent years earlier. In earlier communications, he gave himself the nickname BTK — for “bind, torture and kill.″

Rader ultimately confessed to 10 killings in the Wichita area, which is about 90 miles (144.84 kilometers) north of Pawhuska. The crimes occurred between 1974 and 1991.

He was sentenced in August 2005 to 10 consecutive life prison terms. Kansas had no death penalty at the time of the murders.

Upston said another case that is being re-examined is the death of 22-year-old Shawna Beth Garber, whose body was discovered in December 1990 in McDonald County, Missouri. An autopsy revealed she had been raped, strangled and restrained with different bindings about two months before her body was found. Her remains weren’t identified until 2021.

An Associated Press phone message seeking comment from the McDonald County Sheriff’s Office was not immediately returned Wednesday.

Upston declined to say how many other missing person and homicide cases are being re-examined.

No information has been released yet about what the search Tuesday in Park City uncovered.

Park City Police Chief Phil Bostian told KAKE-TV that Osage County called them as a courtesy and said they asked public works to move some cement and do a little digging.

Police there didn’t immediately return a phone message from the AP seeking comment. Upston said more information would be released later Wednesday.