Editor’s note: This story has been updated to clarify the attendees of a law enforcement interview described by District Attorney Mike Fisher.

WICHITA, Kan. (KSNW) – An Oklahoma district attorney said Monday there was insufficient information to pursue charges against the serial killer known as BTK in an Osage County cold case.

Last month, Osage County authorities said Dennis Rader, the Kansas man convicted of being the BTK serial killer in Wichita, was “a prime suspect” in some unsolved missing persons cases, including that of Cynthia Dawn Kinney, of Pawhuska, Oklahoma.

Last week, the Osage County, Oklahoma, undersheriff said they have at least four “pretty strong connections” to cold case investigations linked to Rader that they feel could go to trial.

On Monday, District Attorney Mike Fisher said he was not at a point where he could press charges against Rader.

“As of this date, the information that has been shared is insufficient to file criminal charges against Dennis Rader,” he said in a press conference. “Given the interest that this information has garnered, I have asked that the Oklahoma State Bureau of Investigation open a formal investigation into the disappearance of Cynthia Dawn Kinney.”

Fisher said he will file charges if he learns of any evidence that warrants it. He said he sat in on a law enforcement interview about Rader about 90 days ago. He said Kansas, Missouri, and Oklahoma investigators took part while Fisher and his investigator listened.

He said the Osage County Sheriff has not shared any physical evidence with the DA’s office.

“The information that we have received to this point, there are – I’ll call them rumors because they’ve not been substantiated yet – rumors as to potential other evidence that I have been made aware of,” Fisher said. “None of that at this point arises to the level of even reasonable suspicion.”

Fisher said he has asked state investigators to open a formal investigation because he wants to make sure information is being gathered appropriately.

“There are certain ways that an investigation is handled, and the things that I have seen give me pause and concern,” Fisher said. “The sheriff and I believe undersheriff went to Mr. Rader’s house with a search warrant, and they actually did a dig there. While I appreciate their enthusiasm, it’s probably not appropriate that they be doing that. It would probably be better left to investigators.”

In the meantime, he said he was concerned for Kinney’s parents. He met with them for about two hours on Friday. He said they are both in their 80s, and the recent 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.”

He said the recent news coverage has her parents considering scenarios of what could have happened to her. They have both lost weight in the past few weeks as a result of the stress, he said, asking people to give them their privacy.

Rader, 78, has been in the El Dorado Correctional Facility since his sentencing in 2005.