Gloria Bobertz is on the hunt for a potential serial killer.

The cousin of 21-year-old murdered victim Kristina Nelson has chosen to come forward on a new Investigation Discovery docuseries titled “Cold Valley,” which explores a string of unsolved crimes and disappearances that occurred between 1979 and 1982 along the border between Idaho and Washington.

The series features emotional interviews with the families of those still missing or deceased, as well as a closer look at Asotin County Sheriff’s Detective Jackie Nichols’ work in revisiting Nelson's and the rest of cases.

At least five young people vanished in the small Lewis Clark Valley, the documentary claims, but only three of those bodies have been found. The other disappearances remained unsolved. While local police worked for years to find the culprit, the cases were shelved due to minimal evidence and leads.

Detective Nichols has been investigating the disappearance of 12-year-old Christina White — the first of the five in the area to go missing — since she became a detective in 2007 with the Asotin County Sheriff’s Department in Washington.

Christina White — ID

On April 28, 1979, White was at a friend’s house when she called her mother to say she felt overheated. Her mother advised her to cool down with a towel and then ride her bike home when she felt better. However, White never made it. Not long after, her school papers were found scattered on the outskirts of Asotin. She has never been found.

Then on June 26, 1981, University of Idaho student Kristin David was ready to embark on a lengthy bike ride from her school in Moscow, Idaho to the Lewis Clark Valley. The 22-year-old never arrived. On July 4th of that same year, a fisherman discovered a garbage bag floating in the Snake River. It contained David’s dismembered body.

The documentary claims Nichols has dedicated “countless hours” in pursuit of the truth, and all the clues point to one man. And while Nichols knows his identity, she cannot reveal it until she is sure she has the evidence to prosecute him in a court of law.

Investigators recover Kristin David's remains from the Snake River. — ID

Bobertz, who has been leading her own investigation in hopes of finding the perpetrator, said she chose to participate in “Cold Valley” to raise awareness on Nelson’s unsolved murder.

“I wanted to do this because I knew it would get out there,” Bobertz told Fox News. “I was really excited that law enforcement would be involved. I thought that was absolutely wonderful. That’s why I decided I wanted to partake and be a representative of our family.”

Asotin County Det. Jackie Nichols. — ID

Lewiston, Idaho’s KLEW TV reported Nelson and her 18-year-old stepsister, Jacqueline “Brandy” Miller, decided to walk to the grocery store on September 12, 1982, only to never be seen alive again. Both women were attending Lewis Clark State College and worked at the Lewiston Civic Theatre.

“Kristina was probably one of the kindest, sweetest people you would ever want to meet,” said Bobertz, 57. “She wanted to become a veterinarian. That change and she decided to go to school and become an accountant. But she was also quite involved with her artwork and she was a really good artist. She had some of her paintings displayed at the Lewiston Civic Theater.”

On the same night Nelson and Miller went missing, authorities learned Steven Pearsall, 35, who also worked at the Lewiston Civic Theater and was friends with the women, also vanished. KLEW TV shared on the night Pearsall disappeared, he had gone to the theater to practice his clarinet and do laundry. Investigators found his car, paycheck and instrument, which his family said he would never abandon.

“They knew each other through the theater,” said Bobertz about the trio. “He was like a big brother.”

Bobertz added her family didn’t know what to make of the sudden disappearances. However, Bobertz said she had a sinking feeling she would never speak to Nelson again.

Steven Pearsall — ID

“When I heard she had gone missing, I knew she was gone,” said Bobertz. “I just knew it. I felt it. I can’t even begin to tell you how much it impacted our family. Families dissolve because of situations like this.”

On March 19, 1984, the skeletonized remains of Nelson and Miller were found in a remote area near Kendrick, Idaho. Lengths of cord were also discovered nearby.

“They were found outside of Kendrick, Idaho right off the side of the highway as it goes off the grade there,” Nichols told KLEW TV. “It was as though they were probably tossed off the side of the grade and rolled down and stopped at the base of a tree.”

Bobertz said she still vividly remembers the day her family got the phone call.

“I remember exactly where I was standing when we were told,” she recalled. “I could even tell you what I was wearing. It was such a shock to know that she was gone in such a violent way. That somebody who was so kind and sweet could have her life end by murder. And Brandy, she’s family. No matter what, I wanted to know why. I guess that’s what has taken me on my journey to find those answers. Because it was a loss of innocence for me. Bad things do happen to young people. We’re not invincible.”

Kristin David (ID)

Pearsall still remains missing. Nichols told Investigation Discovery she believed Pearsall is a victim because “he doesn’t have the personality, really, that fits the profile of someone that would commit the homicides, and by all accounts, he was kind of a [milder], low-key type of person, pretty passive, not prone to anger.”

Nichols believes Pearsall may have “walked in on something horrific happening that he was a witness to, and that was the end of his life right there.”

The network added that a person of interest associated with White’s 1979’s disappearance reportedly admitted to police he was working in the theater around the same time and on that same fateful night all three people vanished. However, he insisted he hadn’t heard or seen anything out of the ordinary.

The person of interest also refused to take a lie-detector test at the time on his attorney’s advice and later moved to North Carolina in the late 1990s.

KLEW TV revealed the Lewiston Civic Theatre has since been condemned and at risk of falling apart.

Brandy Miller (ID)

Bobertz said lack of evidence has made it difficult for authorities to track down answers. However, she’s hoping DNA could finally crack these cold cases. She also suspects there may be more victims.

“I think the person of interest — he committed the crime in the valley ’79-82,” she explained. “And then it would have been harder for him to hide. So I think he went to other areas because he’s extremely intelligent… He would definitely remember the lay of the land.”

In 2017, The Spokesman-Review reported a cold case unit of investigators, prosecutors and staff were formed to review the case and evidence that was collected.

Bobertz is hopeful the documentary will compel those who may have information to come forward with tips. She is also certain that someday, she will learn what really happened to the two young women in her life.

“I do believe I will get answers,” she said. “It may not be in the near future, but I think there will be answers. You can only hide for so long. Your past will come up and bite you. So I always hold out hope that there will be answers and there will be justice.”

Gloria Bobertz has devoted thousands of hours to tracking down leads related to the murder of her cousin Kristina Nelson. — ID

"Cold Valley" premieres Thursday, November 29 at 9 p.m. on ID.