PAWNEE, Okla. (AP) — There isn’t enough evidence to charge the BTK serial killer in the 1976 disappearance of a 16-year-old girl, an Oklahoma prosecutor said Monday despite statements from law enforcement officials calling Dennis Rader a prime suspect.

District Attorney Mike Fisher said at a news conference that he’s not at a point where he could file charges against Rader in the disappearance of Cynthia Dawn Kinney, a cheerleader from the northern Oklahoma city of Pawhuska who was last seen at a laundromat.

But Fisher asked the Oklahoma State Bureau of Investigation to open a formal investigation into Kinney’s disappearance because of the public interest in the revived cold case, and he will file charges if he learns of evidence that would warrant it, he said.

Osage County sheriff’s officials, including Undersheriff Gary Upton, have recently called Rader a “prime suspect” in Kinney’s disappearance and the death of 22-year-old Shawna Beth Garber, whose body was discovered in December 1990 in McDonald County, Missouri.

Rader, now 78, killed from 1974 to 1991, giving himself the nickname BTK — for “bind, torture and kill.” He played a cat and mouse game with investigators and reporters for decades before he was caught in 2005. He ultimately confessed to 10 killings in the Wichita, Kansas, area, about 90 miles (144.84 kilometers) north of Pawhuska. He is imprisoned for 10 consecutive life terms.

A bank was installing new alarms across the street from the laundromat where Kinney was last seen, Osage County Sheriff Eddie Virden has said. Rader was a regional installer for security system company ADT at the time, but Virden wasn’t able to confirm that Rader installed the bank’s systems.

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

Fisher said he sat in on interviews that Kansas, Missouri, and Oklahoma investigators conducted with Rader about 90 days ago, but the sheriff has not shared any physical evidence with the DA’s office.

He called the information he has received so far “rumors because they’ve not been substantiated yet.” And he said he hadn’t seen anything “that at this point arises to the level of even reasonable suspicion.”

But Fisher said he had seen things that gave him “pause and concern” about the sheriff’s department, including the way they handled a dig for evidence at Rader’s former property in Park City, Kansas, last month. And he called his relationship with the sheriff “broken.”

“I’m not trying to create a conflict with the sheriff of Osage County,” he said. “But, there are certain ways to investigate a case, and I’m concerned that those proper investigative techniques have not been used. That’s why I asked the OSBI to assist.”

Virden defended his handling of the investigation in an interview published Sunday in the Tulsa World. He also said Rader denied when he spoke to him in prison in January that he had killed anyone but his 10 victims in Kansas, but volunteered that one of his favorite unfulfilled fantasies had been to kidnap a girl from a laundromat.

The prosecutor said he was also concerned for Kinney’s parents, with whom he met for about two hours on Friday. He said they are both in their 80s, and the renewed speculation has taken a physical toll on them.

“Cynthia went missing 47 years ago. They’ve got no answers,” Fisher said. “We have reason to believe that it may have been a homicide. We can’t say that with any absolute certainty, but we’ve seen nothing to suggest otherwise as there’s been no contact with Cynthia Dawn since 1976, since her disappearance.”