"Are you entering into this plea freely and of your own will?" asked Judge Deno Himonas.
"Yes, sir," answered Hilfiker, a white-haired man who stood facing the judge wearing a white prison uniform and linking his fingers tight behind his back.
Hilfiker will be sentenced in 3rd District Court next month for first-degree felony aggravated murder. He faces up to life in prison.
In exchange for his plea, prosecutors took the possibility of the death penalty off the table and will recommend that Hilfiker's new life term runs concurrently with one he is already serving for an unrelated murder in 1992.
Family members of Rundle found her body inside her home Oct. 22, 1989, after they hadn't heard from her for a few days, according to the Unified Police Department. She had been stabbed and suffered blunt force trauma, according to court records.
Detectives at the time could find no suspects, police wrote. But UPD last year received federal funds to reopen the case and found DNA evidence that was collected from Rundle. The profile matched that of Gary Hilfiker, who is serving time for an unrelated 1992 homicide, according to police.
Investigators learned that Rundle typically used taxis for transportation, and that Hilfiker was a cabdriver who had driven Rundle several times, police wrote.
Hilfiker, interviewed in prison, admitted to killing Rundle, police wrote in court documents. He said he was confronted by Rundle, so he stabbed her and took "a couple hundred dollars" from her purse, police wrote.
The case is one of several cold cases that have been reopened since UPD received a federal grant for $300,000 to investigate old cases that may be solved with new DNA technology.
Prosecutors said Friday that several of the woman's family members may wish to speak at next month's sentencing.
Hilfiker previously was convicted of murder and aggravated arson in the 1992 death of 38-year-old Marsha Haverty, for which he is serving up to life in prison.
Hilfiker stabbed the Haverty woman up to 10 times in her Salt Lake City home, poured kerosene over her and set her body ablaze.
At a 2010 parole hearing, Hilfiker told the Board of Pardons and Parole that he killed Haverty, who was his friend, in a drug-fueled, "discombobulated state" when she tried to talk him out of killing himself.
Hilfiker said he was despondent after a failed romance, and in trying to talk him out of suicide, Haverty and Hilfiker began arguing over Hilfiker's drug use.
The board had given Hilfiker a parole date in 2022.