Steve Pankey was always curious about the case of his neighbor, Jonelle Matthews, a seventh-grader who vanished five days before Christmas in 1984.

It would take over three decades for the police to find out why.

“He was a monster who tapped on the shoulder of law enforcement,” retired lead detective Robert Cash told Fox News Digital. “He taunted law enforcement. But when we put the pieces of the puzzle together, it became clear. His behaviors and his writings – pretty much everything about his character – gave us an indication that his taunting us gave him fuel. It gave him satisfaction to think he had duped law enforcement.”

IDAHO MAN RECALLS HOW ‘EVIL’ ESTRANGED WIFE, A FORMER NURSE, COMMITTED MURDER IN DOC: ‘I FELT DISGUSTED’

“He was a monster who tapped on the shoulder of law enforcement.” 

“It was his constant rehashing and laying these hints … it kept the case alive,” Cash shared. “And thankfully, he tapped on the right shoulder at the right time.”

The case of the 12-year-old Greeley, Colorado, resident is being explored in a two-part special on Oxygen, “The Girl on the Milk Carton.” It features new interviews with Matthews’ family, local police who investigated for almost 40 years, as well as Angela Hicks, Pankey’s ex-wife.

The documentary also details how Hicks played a role in solving the case.

The case of Jonelle Matthews is being explored in an Oxygen true crime special airing Sunday, “The Girl on the Milk Carton.” (Oxygen True Crime)

“I hadn’t done any interviews [before], but I just felt the documentaries I was seeing, and some of the [true-crime] podcasts were just getting things so wrong,” Hicks told Fox News Digital. “It was just so inaccurate. . . . And I felt this documentary would honor Jonelle Matthews.”

Jonelle Matthews’ (left) sister, Jennifer Mogensen (right), remembered Jonelle as “a strong, independent, opinionated 12-year-old.” (Oxygen True Crime)

Matthews was a member of the Franklin Middle School Honor Choir and active at the Sunny View Church of the Nazarene. After performing at a Christmas concert with classmates, she was taken home by a friend and the friend’s father. Her mother was out of state caring for her ailing grandmother, and her father was at her sister’s basketball game.

Matthews was last seen at 8 p.m. on Dec. 20, entering her family’s lit ranch-style home with a detached garage, the front yard blanketed by snow.

FOLLOW THE FOX TRUE CRIME TEAM ON X

Jonelle Matthews disappeared shortly after singing “Jingle Bells” with classmates at a 1984 Christmas concert in Colorado. (Oxygen True Crime)

Hicks, who was married to Pankey at the time, described how they had been coming back from an “impromptu” trip to California. Hicks said they left Big Bear Lake “abruptly” when she first learned of Matthews’ disappearance.

“We were driving, and Steve said, ‘Turn the radio on,’” Hicks recalled. “It was unusual for us, because he had banned radio, TV and newspapers a year before. We didn’t have any of that in our lives. I assumed he wanted me to find some music to listen to, some old ‘50s rock ‘n’ roll. I tried to find that, but he said, ‘No, no.’ He wanted me to put on the news channels. That’s when I heard Jonelle Matthews was missing. That’s what he wanted to hear.”

This photo of Jonelle Matthews’ home was taken shortly after she vanished. (Oxygen True Crime)

“For the rest of Christmas Day and the next day until we got back to Greeley, while we were driving, I was constantly flipping the radio for news about the missing girl,” Hicks shared. “They mentioned Sunny View Church, which Steve was a member of. . . . But it was obsessive. It was him hearing the radio report over and over. Every time we listened to one station he would say, ‘Find another.’ . . . He just felt this strange need.”

Jonelle Matthews was one of the first missing children whose face was printed on milk cartons. (Oxygen True Crime)

Cash said that at the time, Pankey wasn’t a suspect but that he somehow needed to know everything about the investigation.

“Even in the early days of the case, he was the one who reached out to law enforcement,” Cash explained. “But it took decades for him to become a suspect.”

It took decades for Jonelle Matthews’ (left) neighbor to be listed as a prime suspect. (Oxygen True Crime)

According to reports, Pankey inserted himself into the case, quickly raising eyebrows. But there was no evidence to prove he was involved in Matthews’ disappearance.

SIGN UP TO GET THE TRUE CRIME NEWSLETTER

Jonelle Matthews “would have celebrated a happy 13th birthday with her family,” said President Ronald Reagan. “. . . But five days before Christmas, Jonelle disappeared from her home.” (Oxygen True Crime)

Meanwhile, Matthews’ case garnered national attention after President Ronald Reagan took up the case as part of his administration’s attempt to help locate the more than one million children who reportedly disappeared each year. Her picture was printed on milk cartons across the country as part of a project by the National Child Safety Council.

Jonelle Matthews’ at the time she disappeared. (Oxygen True Crime)

Meanwhile, Pankey had brushes with the law and spats with people. A few years after Matthews disappeared, Pankey and his family moved to different states before finally settling in Idaho.

Hicks said their marriage continued to deteriorate over the years.

Over the years, Steve Pankey kept tabs on the investigation of Jonelle Matthews. (Oxygen True Crime)

“Steve had made threats against my father,” she claimed. “. . . I was walking on eggshells, trying to keep the peace. I felt like I had to keep the people I cared about in my life safe. You’re in a domestic violence relationship, a coercive control situation, but it’s like you’re frozen. You feel like there’s nothing you can do without a plan or a support system. I was trapped. And especially when we left Greeley . . . I had no support system whatsoever.”

Jonelle Matthews is seen here as a baby with her family. (Oxygen True Crime)

Prosecutors said that Pankey kept up to date on the case, even as he moved to several other states. In 1999, he told the Idaho Supreme Court, after causing a scene at a bank, that his conviction, which was later dismissed, had been an “attempt to force” him to “become an informant” in Matthews’ disappearance.

That year, Pankey told Hicks that police were “persecuting” him because he wouldn’t “tell them what they want to know about Jonelle Matthews,” 9News reported.

GET REAL TIME UPDATES DIRECTLY ON THE TRUE CRIME HUB

Jim and Gloria Matthews, holding a picture of their daughter, Jonelle, are pictured during a press conference with District Attorney Michael Rouke, right, at the Weld County Courthouse. (Fort Collins Coloradoan-USA Today Network/Imagn)

According to the outlet, Pankey told his wife, “Do you really think I would hurt her when she looked so much like you?”

Their divorce was finalized in 2002.

“They’re sad,” Jonelle Matthews’ sister told The Associated Press about their parents. “They’re grateful for all the hard work the Greeley Police Department has done.” (Oxygen True Crime)

The outlet also noted that when their son was murdered in 2008, Pankey brought up Matthews before the memorial service.

Russell Ross stands outside the former home of Jonelle Matthews in Greeley, Colorado. Ross and his daughter, Deanna, were the last to see Matthews before her disappearance. (Imagn)

Pankey later turned to politics. He ran unsuccessfully as a Constitution Party candidate for Idaho governor in 2014 and in the Republican gubernatorial primary in 2018. Pankey was labeled a person of interest that year after claiming to have information about what happened to Matthews and asking for immunity from prosecution.

Then in 2019, Cash got a call he will never forget.

Lead detective Robert Cash, who is now retired, told Fox News Digital he was determined to find out what happened to Matthews. The missing girl is seen here as a baby with her family during happier times. (Oxygen True Crime)

“We learned there were some remains that had been found – I just had an electric feeling,” he recalled. “There had been other times when remains were found, and we thought maybe this was it, but we were mistaken. But this time, for whatever reason, this felt very unique. I made the trip down to where the remains were. Braces were still affixed to the teeth on the skull. Jonelle had braces when she disappeared. Then we could still see and make out the colors of the different pieces of clothing. It was a whirlwind of emotion and excitement. I was trembling. All hands were on deck.”

Jonelle Matthews had braces at the time of her disappearance. (Oxygen True Crime)

Matthews’ identity was confirmed with DNA technology. Her death was then ruled a homicide. Matthews died from a single gunshot wound to the head, prosecutors said.

“Parents cry out for help, many through letters to me,” President Ronald Reagan told editors in 1985 about the cases of missing children. “But a president can only do so much.” (Oxygen True Crime)

Pankey’s lawyers said that his behavior may have seemed unusual, but they argued that police had not secured hard evidence against him. They also pointed out that investigators had failed to clear an alternate suspect who had died in 2007, the Tribune reported.

Still, law enforcement had no doubt they had Matthews’ killer.

Jonelle Matthews was considered missing until workers digging a pipeline in a rural area near Greeley in July 2019 discovered human remains matching her dental records. (Oxygen True Crime)

In 2022, Pankey was found guilty of felony murder, second-degree kidnapping and false reporting in the disappearance and death of Matthews in 1984, the office of District Attorney Michael Rourke said. A judge sentenced him to life in prison with the possibility of parole in 2040, the Greeley Tribune reported.

This undated photo provided by the Weld County Colorado District Attorney’s Office, shows Steve Pankey, a former longshot candidate for Idaho governor, charged with murder, kidnapping and other counts in the death of Jonelle Matthews, a 12-year-old Colorado girl who went missing in 1984.  He was arrested on Oct. 12, 2020, at his Idaho home.  (Weld County District Attorneys Office via AP)

It was Pankey’s second trial in the case. In 2021, jurors were unable to reach verdicts on the kidnapping and murder charges, and prosecutors decided to put him on trial again.

Hicks, who testified, said that she finally felt “safe.”

“If he had not been found guilty, I truly would not have been safe from then on out,” she said. “So, I felt relief. But for the first time in 30-some years, I’m safe.”

MISSOURI STUDENT, VICTIM OF ‘THE WORST FRATERNITY HAZING INJURY EVER,’ IS ‘ALIVE FOR A REASON’: PARENTS

In this Aug. 12, 2019, photograph, Jennifer Mogensen holds a poster of her adopted sister, Jonelle Matthews, who went missing and whose remains were found in Greeley, Colorado. Steve Pankey was indicted in the 12-year-old’s murder. Mogensen, who was a junior in high school at the time, said she had been playing varsity basketball the night her younger sister disappeared. (AP Photo/David Zalubowski)

The true motive behind Pankey’s act may never be known. But Cash has his theories.

Cash believes that to Pankey, Matthews “was nobody.” She was just “collateral damage” as a result of his anger against his church, one he “despised.”

“All of this was done in retribution of people who, in his mind, had wronged him,” Cash explained. “I think it highlights the callousness of the crime, the absolute lack of empathy or humanness in Steve. . . . And I think that’s what makes it even more tragic. She got in the way of a monster that, even in his act, had so little emotion.”

Jonelle Matthews’ remains were found in 2019. (AP Photo/David Zalubowski)

“As far as introducing or inserting himself into the case, I just think it goes to his neurosis, his feeling that he has to be fed the information. This was his way, I think, that he was able to play the game. I think, to him, this was all a game. If Steve Pankey had said nothing and not inserted himself into the case, then we probably would still be investigating the disappearance of Jonelle Matthews. Steve Pankey revealed himself, and it’s not unusual that suspects in crimes do this.”

Jonelle Matthews has finally been laid to rest. (Oxygen True Crime)

“. . . I want people to understand that it’s never too late,” Cash reflected. “With the right connection, with the right intentions, cases like this can be solved.”