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A man living in the suburbs of Portland, Oregon, has been found guilty in the 1980 cold case murder of a 19-year-old college student after DNA from a piece of chewing gum linked him to the crime.

Multnomah County Circuit Judge Amy Baggio on Friday found Robert Plympton, 60, guilty of first-degree murder in the death of Barbara Mae Tucker, the Multnomah County District Attorney’s Office said in a news release on Monday.

Plympton was not convicted of rape or sexual abuse because prosecutors failed to prove beyond a reasonable doubt that it happened while she was still alive, the judge said. A medical examiner determined Tucker had been sexually assaulted and beaten to death.

In 2021, a genealogist with Parabon Nanolabs using DNA technology identified Plympton as likely linked to the DNA in the case. Detectives with the Gresham Police Department who found Plympton living in Troutdale, began conducting surveillance and collected a piece of chewing gum he had spit onto the ground, according to prosecutors.

Police arrested Plympton after the Oregon State Police Crime Lab determined the DNA profile developed from the gum matched the DNA profile developed from swabs taken from Tucker’s body, which had been preserved.

Tucker was expected at a night class at Mt. Hood Community College in Gresham on Jan. 15, 1980. Witnesses said she had been seen running out of a bushy, wooded area on campus and that a man came out of the area and led her back to campus. A student found Tucker’s body the next day near a campus parking lot.

The business student had been sexually assaulted and beaten to death, CBS affiliate KOIN-TV reported.

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

Plympton said he was innocent and that he didn’t match the description of a man seen pulling her into the bushes.

He is scheduled to be sentenced in June.

Tucker’s family told KOIN-TV in 2021 it was an emotional moment when they received the news that Plympton had been arrested.

“Just not giving up. We always had hope,” said Tucker’s sister, Susan Pater. “At one point we though he was dead. Maybe it would never be solved. I just wished it could have happened when the rest of my family was here, especially my parents.”

Detective Aaron Turnage told them he wouldn’t rest until the case was solved.

“I promised her I was going to solve this case. If that means working around the clock, that’s what happens,” the detective told the station. “There has been lots of hurdles and sitting down and experiencing that with the family last night is something I’ve never experienced in my career. It’s pretty awesome.”