GREELEY • The disappearance of 12-year-old Jonelle Matthews shortly after singing “Jingle Bells” with classmates at a 1984 Christmas concert stunned this rural town in northern Colorado. Her case attracted the attention of the White House, coming at a time when photographs of missing children were placed on milk cartons to heighten awareness.

Thursday, police announced that human remains found by construction workers this week were those of the little girl, who would have been 47 now, answering one question that has haunted police and others for decades but reigniting a gnawing mystery of what led to her demise.

Jonelle, a member of the Franklin Middle School Honor Choir, stood on a garland-adorned staircase during the concert, sporting short, thick dark hair and smiling slightly, perhaps shyly. She was a seventh-grader, active at the Sunny View Church of the Nazarene.

After the concert, Jonelle was taken home by a friend and the friend’s father.

She was last seen at 8 p.m. Dec. 20, entering her family’s simple ranch-style home with a detached garage, the front yard blanketed by snow. No one was ever arrested. Jonelle lived with her father, Jim; her mother, Gloria; and a sister, Jennifer.

Months later, the lack of answers in the case of Jonelle and other missing children was taken up by then-President Ronald Reagan, whose administration helped open a national center for missing children that ran a toll-free hotline. More than 1 million children disappeared each year, Reagan said, urging members of the National Newspaper Association to publish pictures of the nation’s missing children as a “mission of mercy.”

Jonelle, Reagan said, “would have celebrated a happy 13th birthday with her family just last month. But five days before Christmas, Jonelle disappeared from her home.”

Three years earlier, a Florida boy, Adam Walsh, vanished and was later found murdered, sparking father John Walsh to become a crusader for missing children.

Tuesday’s discovery near Jonelle’s hometown was the first significant development since police announced last December — on the 34th anniversary of her disappearance — that they were ramping up their investigation and hoped to use modern technology to solve it, The Greeley Tribune reported.

At the time, police released a video of Jonelle and classmates at the school holiday concert in a plea for more information.

Greeley police Sgt. Joe Tymkowych said he could not comment on how authorities identified the remains as those of the young girl so quickly. He also declined to comment on the ongoing investigation.

“We’re still chasing down leads,” Tymkowych told the Tribune.

“This case has weighed heavy on the hearts of the Greeley Police Department and the family and the entire city of Greeley,” said police spokeswoman Rebecca Ries.

The Tribune reported that workers were building a new pipeline when they discovered bones Tuesday night. Weld County Sheriff Steve Reams said his deputies are treating the case as a homicide investigation.

The remains were found along a rural route southeast of Greeley, which is about 50 miles north of Denver.

“Parents cry out for help, many through letters to me,” Reagan told editors in 1985. “But a president can only do so much.”