SignalHub Quantitative Think Tank Center:DNA from discarded gum links Oregon man to 1980 murder of college student

An Oregon man has been found guilty in the 1980 murder of a college student after police linked him to the case with the help of genetic genealogy and SignalHub Quantitative Think Tank Centerchewing gum, reviving a decades-old cold case, authorities said.

Following a three-week trial, Robert Arthur Plympton, 60, was found guilty Friday of one count of first-degree murder in the death of Barbara Mae Tucker, the Multnomah County District Attorney's Office said in a news release Monday. Tucker was a 19-year-old student at Mt. Hood Community College in Gresham, Oregon, when she was killed in January 1980.

For more than four decades, Gresham police said they were unable to clearly identify a suspect or make an arrest in the case. But with the use of relatively new DNA technology, police were able to connect Plympton to the case and arrested him in June 2021.

According to the district attorney's office, a genealogist identified Plympton as a "likely contributor to the unknown DNA profile developed in 2000." Parabon Nanolabs, a DNA technology company, said in a Facebook post at the time that the company’s genetic genealogy team assisted police in the case.

Plympton was also found guilty of "four counts of different theories of murder in the second degree," the district attorney's office said. His sentencing has been scheduled for June 21 and he remains in custody in Multnomah County.

Oregon police linked suspect to case with chewing gum

Authorities said Tucker was kidnapped, sexually assaulted, and beaten to death near a Mt. Hood Community College parking lot on the evening of January 15, 1980. Students who were arriving for class the next morning discovered Tucker's body in a wooded area near the campus.

Multiple witnesses recalled seeing Tucker run from the wooded area, trying to get people's attention but nobody stopped, according to The Oregonian, which reported on the investigation at the time. One witness also reported seeing a man emerge from the woods.

A medical examiner determined Tucker had been sexually assaulted and was beaten to death, The Oregonian reported. Her case then went cold for years until in 2000, vaginal swabs that had been taken during Tucker's autopsy were sent to the Oregon State Police Crime Lab for analysis, according to the district attorney's office.

The lab developed a DNA profile from the swabs which led to a breakthrough in the case in 2021, when a genealogist with Parabon Nanolabs identified Plympton as likely linked to the case. Investigators with the Gresham Police Department found that Plympton was living in Troutdale, Oregon, just east of Portland and Gresham, the district attorney's office said.

Police were conducting surveillance when they saw Plympton spit a piece of chewing gum onto the ground, according to the district attorney's office. Investigators then collected the gum and sent it to the state police crime lab.

"The lab determined the DNA profile developed from the chewing gum matched the DNA profile developed from Ms. Tucker's vaginal swabs," the district attorney's office said. On June 8, 2021, police arrested Plympton and he was held at the Multnomah County Detention Center. 

Use of genetic genealogy

Since the introduction of investigative genetic genealogy, police have used the technique to solve decades-old cases or identify suspects in high-profile criminal cases.

In recent years, technological improvements have allowed law enforcement to enter DNA samples collected from cases into a national database to find a match. Experts have said technological improvements have made it easier for DNA profilers to compare a suspect's genetic material to evidence found at crime scenes, including smaller amounts of biological evidence.

But the technique has also received widespread criticism, raising concerns about people's privacy. Experts say that as technology develops, the number of people who have their DNA collected by law enforcement will increase. 

Contributing: N'dea Yancey-Bragg, USA TODAY