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(NewsNation) — Kerri Rawson, the daughter of Dennis Rader, otherwise known as the “BTK Killer,” says there is “mounting evidence” her father is behind the disappearance of missing 16-year-old Oklahoma girl Cynthia “Cindy” Dawn Kinney.

However, she told NewsNation’s Brian Entin in an interview that the case is still “under investigation” and the evidence is “circumstantial.” Rawson said that what’s most important is that “we need to find Cindy.”

The Osage County Sheriff’s Office has a working theory that Rader was involved with Kinney’s kidnapping, and he’s been investigated as a suspect. Last June, Rawson started helping them as well, working through her dad’s evidence and even seeing him in prison. 

“There’s been a lot of effort in trying to locate where she may be, no matter what happened to her,” Rawson said of the teenager, who vanished from the Osage Laundry in June 1976, according to NewsNation local affiliate KFOR.

Cops say they found items linked to BTK

Last August, police recovered pantyhose and other “items of interest” while searching BTK’s former Kansas property, according to Osage County Sheriff Eddie Virden.

 Virden, who led the search team, said the items found were “significant.”

“We believe he’s tied in with our case and our prime suspect and possibly on several other cases in Kansas and one in Missouri,” Virden said at the time.

In April of this year, the Osage County Sheriff’s Office received a package from an anonymous woman containing a word puzzle BTK sent to a Kansas news station in 2004, according to KFOR.

“There’s hints all the way through that can’t be overlooked,” Virden said.

In 2004, there were a handful of the words identified in the puzzle: “Wichita,” “prowl,” “fantasies,” “ruse,” “spot victim” and “serviceman.” Upon looking at it again, authorities discovered the words:

• Cindy
• Kinney
• Osage
• Laundry Mat
• Kihekah (the name of the street where Osage Laundry is located)
• Elgin
• Pawhuska
• Oklahoma
• Cleveland

In addition, the puzzle spells out the names of Rader’s ten known victims and Rader’s home address in Kansas.

KFOR reported that markings in journal entries made by Rader also indicate where he traveled and why. Some markings appear to show that Rader traveled to Oklahoma for a vacation, a Boy Scouts trip, business or other reasons.

It was through working with the Osage County Sheriff’s Office that Rawson says she found evidence of her father sexually abusing her, which she talked to NewsNation’s Brian Entin about at CrimeCon in Nashville, Tennessee. 

Who was the BTK Killer?

Rader was the one who gave himself the “BTK” nickname, which stands for “Bind, Torture, Kill.” 

Authorities say he first killed in 1974, stoking fears throughout the 1970s in the Wichita, Kansas, area. Rader, a former Air Force sergeant who was married with two kids, lived in the Wichita area almost his entire life.

Before his 2005 conviction on charges that he killed 10 people from 1974 to 1991, Rader led investigators and the media on a cat-and-mouse game. Authorities still believe there are multiple missing persons cases connected to him.

His daughter, Rawson, has been helping law enforcement as they conduct their investigations and worked as a victim advocate. She has written two books: “A Serial Killer’s Daughter: My Story of Faith, Love and Overcoming” and “Breaking Free: Overcoming the Trauma of My Serial Killer Father.”

The Associated Press contributed to this report.