WICHITA, Kan. (KSNW) — After searching the former property of the BTK serial killer, authorities from Osage County, Oklahoma, say there might be connections to other missing person cases.

Investigators named Dennis Rader as the No. 1 suspect in an Oklahoma missing person case from the 1970s. He also has been named the “prime suspect” in an unsolved killing in Missouri, authorities announced Wednesday.

The Osage County Sheriff’s Office said the focus of Tuesday’s search in Park City, Kansas, was closely tied to the disappearance of Cynthia Dawn Kinney of Pawhuska, Oklahoma. The 16-year-old cheerleader was last seen leaving a laundromat in Pawhuska in June 1976.

The sheriff’s office said they started investigating the case again in December after new discoveries tied Rader to Kinney’s disappearance.

Nearly 50 years ago, investigators suspected Rader was installing security equipment at a bank in Pawhuska, Oklahoma. Across the street was a laundromat where Kinney was last seen. Rader was a regional installer for ADT at the time, although the sheriff wasn’t able to confirm that Rader installed the systems.

According to Osage County Sheriff Eddie Virden, the Park City search was launched this week after deputies received a tip. He said he decided to investigate when he learned that Rader had included the phrase “bad laundry day” in his writings.

“He would go to a laundromat in Wichita and watch victims and young women,” Virden said.

That passage was written in 1976, the same year Kinney disappeared.

“She was taken mid-morning in the week,” Virden said. “A lot of his crimes occurred between 8 and noon in the week when he worked for ADT.”

Other writings from Rader described the place where he buried items belonging to victims: under his storage shed.

“We had developed some information that Dennis Rader had sent to someone describing where he had placed some items from some of his crimes that have never been found,” said Virden. “Originally, at that spot, there was a storage building, and in 2006, our understanding, it was removed from the property along with everything else there. So there had been a building there prior, and when we obtained this information, which came out of a communication with a law enforcement person back years ago, he described having some trophies, souvenirs, and some victims’ driver’s licenses hidden in this location that weren’t found.”

After talking with the Kansas Bureau of Investigation and Park City, deputies, with the help of the city, cut and removed the concrete from the search area.

“We found two different locations where objects had been buried. … Both of them were probably 14-16 inches under ground level,” said Virden.

The first location appeared to include a makeshift time capsule made with a brick, composition shingle roofing, pebbles or stones, a shingle, and dirt. The second location had been filled with a sand-type substance.

Deputies called what was found “items of interest,” saying they would undergo a thorough examination to determine the relevance to Kinney’s disappearance.

“We found some more personal-type items and maybe some more restraint-type items in those locations,” said Virden.

This is the second time this year that deputies have been to Rader’s former residence. The first time was in April, when Osage County law enforcement dug up the site where the shed once stood and found “pantyhose ligature” they believe Rader used to tie up victims.

Osage County Undersheriff Gary Upton said Rader is also the prime suspect in 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.

Rader killed from 1974 to 1991, giving himself the nickname BTK — for “bind, torture and kill.”

Virden said Rader has been cooperative with law enforcement, though he added that “he’s pretty notorious for playing cat-and-mouse games.”

“The investigation is continuing, and you know we got other information of other locations that we plan on in the future. Again, we’re working with those other agencies and trying to mainly get the answers on our case, but if we have any help that can help anybody else on any of their unsolved cases, we hope to get that information to them and get some closure to other people as well as possible,” said Sheriff Virden.

Rader maintains he had no involvement in Kinney’s disappearance.

Rader, now 78, ultimately confessed to 10 killings in the Wichita area, which is about 90 miles north of Pawhuska.

He was sentenced in August 2005 to 10 consecutive life prison terms. Kansas had no death penalty at the time of the murders. His earliest possible release date is listed for the year 2180.

The Associated Press contributed to this report.