PORTLAND (AP) — The Marion County district attorney’s office has declined to prosecute a serial rapist who allegedly threatened a woman who is fighting against his release from prison.

Deputy District Attorney Paige E. Clarkson said the alleged threat made by Richard Gillmore would be impossible to prove beyond a reasonable doubt because it was only overheard by inmates. The law requires it to be made telephonically, electronically or in written form.

“While it does not meet the legal threshold required for criminal prosecution, it is cause for deep concern for public safety,” Clarkson said in a statement.

Gillmore, known as the “Jogger Rapist,” committed at least nine sexual assaults in the 1970s and 1980s. He is seeking parole after more than 20 years in prison.

Two inmates said they heard Gillmore make a threat against Tiffany Edens, who was 13 when she was raped by Gillmore in 1986.

Last year, the parole board twice cleared Gillmore for release, but Edens teamed with the Multnomah County district attorney’s office to file a lawsuit that kept him behind bars.

The three-member Oregon Board of Parole put its latest review of Gillmore on hold while the Oregon State Police investigated the alleged threat.

On Wednesday, the board’s executive director said members will resume the process after the Department of Corrections decides whether to discipline Gillmore.

Two inmates reported overhearing Gillmore threaten to “cut the bitch’s throat,” said Jim McIntyre, who is Edens’ attorney. McIntyre told The Oregonian newspaper that Gillmore did not mention Edens by name but aimed the threat at the woman “who was ruining his chances for parole.”

Gillmore and the two inmates were interviewed, said Lt. Gregg Hastings, spokesman for the Oregon State Police. Gillmore denied making the threat.