NEWYou can now listen to Fox News articles!

More than three decades after the torture, mutilation and murder of Tennessee 19-year-old Colleen Slemmer, former Knoxville Police Chief Phil Keith says he's still haunted by the "satanic" crime scene.

"I'll remember this case to the day I die," he told Fox News Digital Thursday. Keith had been the city's chief of police from 1988 until 2004 and spent decades in law enforcement.

Led by then-18-year-old Christa Pike, three classmates from a vocational school for troubled youths, the Knoxville Job Corps Center, lured Slemmer to her death by claiming they want to go to a music store and pick up marijuana they'd stashed in a park.

CHRISTA PIKE'S ATTORNEYS SAY SHE'S IN CRITICAL CONDITION AFTER BOTCHED LETHAL INJECTIONS

Christa Pike wearing white with curley red hair at trial in 1996

Christa Gail Pike is seen during her trial for the murder of Colleen A. Slemmer March 18, 1996, in Knox County Criminal Court. (USA TODAY Network via Reuters Connect)

"She represents pure evil," Keith said of Pike.

They tortured Slemmer for nearly an hour, Keith said, beating, cutting and gagging her before crushing her skull against the ground with a chunk of broken asphalt.

When she tried to escape, they held her down. When she begged for her life, they slashed her with blades. And when she cried, they gagged her with a hair tie. Pike, 18 at the time and now 50, kept a fragment of her skull as a trophy and showed it off to classmates before her arrest. Her boyfriend at the time, who was also convicted but did not face the death penalty because he was only 17, carved pentagrams into her chest and face.

TENNESSEE DEATH ROW INMATE SURVIVES 2 LETHAL INJECTION DOSES IN FAILED EXECUTION ATTEMPT

Colleen Slemmer in a portrait photo.

An undated portrait photograph of Colleen Slemmer provided by her mother. (May Martinez/Special to the News Sentinel)

At trial, an expert said the attack had "satanic elements" and also involved "the phenomenon of collective aggression, in which a group of people become emotionally aroused and 'the end result is that they engage in some kind of violent, extremely violent activity,'" court records show.

The University of Tennessee groundskeeper who found her remains testified at trial that he initially thought he'd come across an animal carcass before he saw the victim's clothes through the blood, according to court records.

FOLLOW THE FOX TRUE CRIME TEAM ON X

Dr. Murray Marks holds the victim's shattered skull at Christa Pike's murder trial in 1996

University of Tennessee forensic anthropologist Dr. Murray Marks testifies about the wounds to Colleen A. Slemmer's skull during Christa Gail Pike's murder trial in Knox County Criminal Court on March 25, 1996. (USA TODAY Network via Reuters Connect)

"[The images] are as vivid today as the day I saw them," Keith said. "All I have to do is shut my eyes, and I can see everything."

Thirty-one years later, he said he wishes that the Knoxville Police Department had used modern post-trauma therapy counseling at the time.

SIGN UP TO GET THE LATEST TRUE CRIME NEWS

"We didn't have therapy services or counseling or anything at that time, and we, I wish we had, because these images will never be erased," Keith said.

CLICK HERE FOR MORE FROM THE FOX TRUE CRIME HUB

Pike was scheduled for execution on Wednesday. The U.S. Sixth Circuit Court of Appeals, issued a brief stay amid a last-minute appeal, but the Supreme Court lifted the stay and cleared the way for her to face lethal injection.

SEND US A TIP

After two doses, she remained alive. She spent Thursday in an undisclosed hospital in critical condition and receiving "lifesaving care," according to her attorneys, who then said on Friday that she was unconscious and on a ventilator.

"Christa remains critically ill and is receiving medical care for the devastating effects of Wednesday night's events," attorneys Stephen Ferrell and Luke Ihnen said in a statement Friday. "As detailed in today's filing, Christa remains hospitalized following Wednesday night's failed execution attempt.

"She is critically ill, unconscious, intubated and receiving breathing assistance through a ventilator," they added. "She is being treated for the serious effects of the pentobarbital administered during the execution attempt, including significant injuries to both arms."

What she may face next remained unclear.

LISTEN TO THE NEW 'CRIME & JUSTICE WITH DONNA ROTUNNO' PODCAST

WATCH: Christa Pike's attorney responds to botched execution's impact on victim Colleen Slemmer's family

GET BREAKING NEWS BY EMAIL

Randy Spivey, one of Pike's attorneys, responded during a news briefing Thursday by revealing that Slemmer's mother was on Pike's mind in the hours before her scheduled execution.

CLICK HERE TO DOWNLOAD THE FOX NEWS APP

"I cannot imagine what this was like for the family of Ms. Slemmer, or anyone who loves that family or is close to that family — or anyone who loves Christa or is close to Christa," he said. "This is awful, and this kind of thing should never happen again."