On Dec. 19, 1979, Michelle Martinko, 18, left a school banquet and drove her family's car to the Westdale Mall in Cedar Rapids, Iowa, to buy a winter coat, Cedar Rapids police said. The next day, she was found stabbed to death in the mall parking lot.
This "tragic case" had been "haunting this community for 39 years," Cedar Rapids Police Chief Wayne Jerman said Wednesday. Investigators struggled over the years to connect DNA collected at the scene to a suspect.
"I cried a lot and I looked out windows all hours of the night," Martinko's mother, Janet Martinko, told Cedar Rapids' CBS station in 1987. "I talked to myself and didn't know what to do ... Then you have to pray."
Thirty-nine years to the day after she was killed, a suspect was charged thanks to DNA and genetic genealogy.
Jerry Lynn Burns, 64, was arrested on Wednesday after police said he was linked by DNA from blood found on Michelle Martinko's clothing and elsewhere in the car at the crime scene.
Dave Franzman, a longtime reporter at ABC Cedar Rapids affiliate KCRG, even covered the case at the time of Michelle Martinko's killing.
"I did not see this day coming," Franzman said on a broadcast this week.
The first piece of progress in the case came in 2006 when a sample of the suspect's DNA from Michelle Martinko's car was submitted to a lab for processing, police said.
The DNA was uploaded to the law enforcement database called Combined DNA Index System, or CODIS, but investigators never found a match, police said.
In 2017, Cedar Rapids police said they reached out to Parabon NanoLabs to help build a suspect profile based on the crime scene DNA.
Parabon made predictions for "ancestry, eye color, hair color, skin color, freckling, and face shape," police said, and the department released the composite images to the public in May 2017.
But it was another technique from Parabon -- genetic genealogy -- that led investigators to Burns, CeCe Moore, Parabon's chief genetic genealogist, told ABC News.
With genetic genealogy, an unknown killer's DNA from a crime scene can be identified through his or her family members, who voluntarily submit their DNA to a genealogy database. This allows police to create a much larger family tree than databases like CODIs.
"In a genetic genealogy database we can reverse engineer the [suspect's family] tree from their distant" relatives who have submitted DNA, Moore said. "So it doesn't matter that they haven't had their DNA tested through another arrest or crime scene, we don't need their DNA. We need somebody from their family to have tested in order to resolve these cases."
The new technique, started this year with the "Golden State Killer," has identified over two dozen suspects.
After tracing the suspect's family tree, investigators zeroed in on Burns, covertly collected his DNA and sent it to a lab for analysis, according to Moore and Jerman.
The lab determined that the DNA collected from Burns was a match to DNA from the blood found on Michelle Martinko's clothing and was consistent with the DNA profile developed from blood found elsewhere in the car, Jerman said.
On Wednesday, after weeks of "planning and strategizing," investigators interviewed and arrested Burns for first-degree murder, Jerman said.
When Burns, of Manchester, Iowa, was questioned, he "denied committing the offense but could offer no plausible explanation why his DNA would be found at the crime scene," police said.
Burns made an initial court appearance via video Thursday morning and said he would fill out an application for a court-appointed counsel. The judge ordered a $5 million cash bond, and Burns is set to return to court for a preliminary hearing on Dec. 28.
"The family never gave up hope that this case would be solved," Jerman said in a statement Wednesday.
"I am thrilled for her sister, Janelle, and wish her parents were alive to see this," Michelle Martinko's high school friend, Elizabeth Laymon, told The Des Moines Register. "I am happy Michelle finally gets justice."
ABC News' Matt Foster and Ahmad Hemingway contributed to this report.