The BTK serial killer has been named the “prime suspect” in two unsolved killings — one in Oklahoma and another in Missouri — leading authorities to dig this week near his former Kansas property in Park City, authorities announced Wednesday.

Osage County, Oklahoma, Undersheriff Gary Upton told The Associated Press 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, a 16-year-old cheerleader in Pawhuska. The case, which was investigated on and off over the years, was reopened in December.

Sheriff Eddie Virden told KAKE-TV that a bank was having new alarms installed across the street from the laundromat where Kinney was last seen. Radar was a regional installer for ADT at the time, although the sheriff wasn’t able to confirm that Rader installed the systems. He also was involved in Boy Scouts in the area.

Virden said he decided to investigate when he learned that Rader had included the phrase “bad laundry day” in his writings.

Upton, the undersheriff, 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.