A guilty verdict in a 32-year-old cold case in Washington state is being hailed as the first of its kind in the US.

William Talbott II was identified as a suspect in the case last year through DNA and genetic genealogy. No other case like it had ever before gone to trial, Fox News reports.

William Talbott II is helped to a wheelchair after being found guilty of a double-murder in 1987. Picture: APF
William Talbott II is helped to a wheelchair after being found guilty of a double-murder in 1987. Picture: APF

The jury verdict found Talbott guilty of murder in the 1987 deaths of a young couple from Canada, Jay Cook, 20, and Tanya Van Cuylenborg, 18, who was also raped.

Talbot was convicted using a practice that involves identifying suspects by entering crime-scene DNA profiles into public databases that people have used for years to fill out their family trees.

A professional genealogist, CeCe Moore, who helps families find distant relatives built a family tree using DNA taken from Van Cuylenborg's pants and determined that the source must be a male child of William and Patricia Talbott.

William Talbott II, now 56, was their only son. He was 24 at the time of the killings and lived near where Cook's body was found.

Genealogist CeCe Moore. Picture: Twitter
Genealogist CeCe Moore. Picture: Twitter

Detectives tailed Talbott, a truck driver, and saw him discard a coffee cup. They tested the DNA left behind, confirming it matched that found on the pants. They say he also matched a palm print from the rear door of the couple's van.

Van Cuylenborg and Cook disappeared in November 1987. Picture: Supplied
Van Cuylenborg and Cook disappeared in November 1987. Picture: Supplied

Van Cuylenborg and Cook disappeared in November 1987 during what was supposed to be an overnight trip from their hometown of Saanich, British Columbia, to Seattle, to pick up furnace parts for Cook's father's business.

William Talbott II, centre, was found guilty in the 1987 killings of a young Canadian couple using DNA and genealogy. Picture: AP
William Talbott II, centre, was found guilty in the 1987 killings of a young Canadian couple using DNA and genealogy. Picture: AP

After a frantic week for their families, Van Cuylenborg's body was found down an embankment in rural Skagit County, north of Seattle. She had been shot in the back of the head.

Hunters found Cook dead two days later next to a bridge over the Snoqualmie River in Monroe - about 95km from where his girlfriend was discovered. He had been strangled with twine and dog leashes.

Over the next three decades, detectives investigated hundreds of leads, to no avail.

John Van Cuylenborg, centre, surrounded by family and friends await the verdict of William Talbott II. Picture: APF
John Van Cuylenborg, centre, surrounded by family and friends await the verdict of William Talbott II. Picture: APF

But in 2017, Snohomish County sheriff's detective Jim Scharf learned about Parabon Labs in Reston, Virginia, which was using a new DNA processing method to extract more information from samples. CeCe Moore, a genealogist there who is known for her work on the public television series Finding Your Roots, was using the more robust genetic profiles to find distant relatives using the public genealogy database GEDmatch.

Washington State Patrol forensic scientist Angela Hilliard talks about a palm print of William Talbot II during his trial. Picture: AP
Washington State Patrol forensic scientist Angela Hilliard talks about a palm print of William Talbot II during his trial. Picture: AP

In 2018, investigators in California used this technique to arrest and charge a man with being the sadistic attacker known as the Golden State killer who killed 13 people and raped nearly 50 women during the 1970s and 1980s. He is yet to go to trial.

Talbott, 56, appeared stunned when the guilty verdict against him was announced.

"It may have been justice delayed but not justice denied for Tanya and Jay," said Tanya's brother, John Van Cuylenborg, the station reported.

Laura Baanstra, sister of Jay Cook, is held by her husband after Talbott was found guilty. Picture: AP
Laura Baanstra, sister of Jay Cook, is held by her husband after Talbott was found guilty. Picture: AP

Talbott was identified as a suspect after DNA from the crime scene was uploaded to the public genealogy website GEDMatch. The DNA led to two second cousins of Talbott with similar DNA and then to Talbott after a family tree was constructed.

Detectives obtained Talbott's DNA after they saw him discard a coffee cup. His DNA matched the crime scene DNA, police said.

In an exclusive interview with The Sun last year, CeCe Moore said: "I got the case on a Friday night. Saturday morning there were matches and by Monday we had given the name of William Earl Talbott to the police.

"The detectives were pretty much in shock.

"We were looking for living people who would fit the suspect's profile. Two of the closest matches converged - intersected into a marriage - and from that marriage there was only one son.

"That led us to only one person who could carry this mix of DNA - William Earl Talbott. We then pointed detectives towards him.

William Talbot II was not even on the radar of police before genealogical testing of his DNA. Picture: Supplied
William Talbot II was not even on the radar of police before genealogical testing of his DNA. Picture: Supplied

"I was hesitant at first as I knew participants in the databases weren't aware police could use their DNA in this way. That changed with all the publicity surrounding the Golden State Killer arrest. It gave people the opportunity to remove their DNA if it was something they did not want it used for."

The victims' families were very grateful that DNA and genealogy had finally helped bring the killer to justice.

"This would not have been solved had it not been for the DNA evidence," said Cook's sister, Laura Baanstra. "The use of GEDMatch, I hope more people will be willing to allow their DNA on websites so this world can be safer."

Talbott's lawyers argued that the DNA evidence against their client did not make him a killer, but prosecutors said the verdict should serve as a warning to other killers.

"Folks aren't going to get away with murder anymore when we have this information," prosecutor Adam Cornell said. "If you're a killer and you're out there, then this office and other law enforcement around the country may be coming for you."