"Always in the back of your mind you might have a little bit of hope," said Jennifer Mogensen, her sister. "We're extremely grateful we're getting this next step toward justice."
Mogensen was a few years older, and she doesn't remember Pankey.
In the decades since he lived in Colorado, he has run as a Constitution Party candidate for Idaho governor in 2014 and in the Republican primary in 2018. It's the same year authorities said he became a person of interest in the girl's death.
He did not immediately return phone or email messages on Tuesday from The Associated Press. But last week told the Times-News in Twin Falls, Idaho, that he was being framed in the case. He said his family had few connections to Jonelle or her family.
The two families did worship at the same church in Greeley, Colorado, and Pankey had made statements to police revealing "intimate knowledge about the commission of the crime" that was not public information, Rourke said.
Pankey had watched children from Jonelle's middle school walk home, according to charging documents. In 2008, his former wife heard him say at his son's funeral: "I hope God didn't allow this to happen because of Jonelle Matthews," prosecutors wrote.
Jonelle disappeared on December 20, 1984, after being dropped home by a friend and the friend's father. She was last seen at 8pm, entering the ranch-style home where she lived with her father, Jim; mother, Gloria; and sister.
But when her father returned from her older sister's basketball game an hour later, Jonelle was gone.
The case came to the attention of then-President Ronald Reagan as his administration launched a national effort to find missing children. Her picture was printed on milk cartons across the US as part of a project by the National Child Safety Council.
"For over three decades, the disappearance of Jonelle Matthews has left our community with many unanswered questions and a void that has not been filled. With the arrest of Steve Pankey ... some of these questions are starting to be answered," said Greeley police department Chief Mark Jones.
Jonelle was considered missing for more than 30 years until workers digging a pipeline in July 2019 discovered human remains matching her dental records in a rural area southeast of Greeley, a city about 80km north of Denver. Police then labelled her death a homicide.
Pankey has been a person of interest in the case, and last year he contacted the Idaho Statesman to tell his side of the story, fearing a possible arrest.