An Oregon man has been found guilty of murdering a college student in 1980 after he was linked to the case decades later by DNA genetic genealogy and chewing gum he discarded.

Robert Plympton, 60, was found guilty of one count of first-degree murder in the death of Barbara Mae Tucker, who was a 19-year-old student at Mt. Hood Community College when she was kidnapped, sexually assaulted and beaten to death near campus four decades ago, the Multnomah County District Attorney’s Office said Monday in a news release.

For years, no one knew who killed Tucker.

She was killed on Jan. 15, 1980, and her body was found the following morning in a wooded area between Kane Road and a school parking lot in Gresham, Oregon, by students arriving for class, the district attorney’s office said.

While her case was cold for years, investigators gave the case a fresh look with advances in DNA technology.

In 2000, DNA swabs taken during her autopsy were sent to the Oregon State Police Crime Lab for analysis, and a DNA profile was made from the swabs.

Then in 2021, a genealogist from Parabon Nanolabs identified Plympton as the likely “contributor to the unknown DNA profile developed in 2000,” the release said.

Police in Gresham found that Plympton was living in Troutdale and began to surveil him.

When they observed him spit out a piece of chewing gum onto the ground, detectives collected the gum and submitted it to the crime lab for analysis.

“The lab determined the DNA profile developed from the chewing gum matched the DNA profile developed” from Tucker’s 2000 DNA swabs, the district attorney’s office said.

Plympton was ultimately arrested on June 8, 2021. He had pleaded not guilty to charges of murder.

Multnomah County Chief Deputy District Attorney Kirsten Snowden previously said there was no evidence that Tucker and Plympton knew each other, The Oregonian reported.

Following a bench trial from Feb. 26 to March 15, Judge Amy Baggio found Plympton guilty of murder and “four counts of different theories of murder in the second degree,” the district attorney’s office announced.

Though the medical examiner determined Tucker had been sexually assaulted, Plympton was not convicted of rape or sexual abuse because prosecutors failed to prove beyond a reasonable doubt it happened while he was alive, the judge said, according to The Associated Press.

He remains in custody in Multnomah County with sentencing set for June 21.

NBC News has reached out to an attorney for Plympton for comment.