The Associated Press

EVERETT — A jury has convicted a Sea Tac man of the killings of a young Canadian couple more than three decades ago — a case that was finally solved when investigators turned to powerful genealogy software to build a family tree of the then-unknown suspect.

Tanya Van Cuylenborg, 18, and her 20-year-old boyfriend, Jay Cook, disappeared in November 1987 after leaving their home near Victoria and crossing the Strait of Juan de Fuca on the Coho ferry to Port Angeles for what was supposed to be an overnight trip to Seattle. Their bodies were found in separate locations in northwestern Washington state about a week later.

On Friday, a jury convicted William Earl Talbott II, a construction worker and truck driver who was 24 at the time of the killings and lived near where Cook’s body was discovered.

Investigators preserved DNA evidence that was recovered from Van Cuylenborg’s body and pants, but they didn’t know whose it was until last year. Authorities used genetic genealogy to identify Talbott.

The genealogy technique has revolutionized cold-case investigations across the U.S. in the past year. It involves entering crime-scene DNA profiles into public genealogy databases, finding relatives of the person who left the DNA and building family trees that lead detectives to a suspect.

Talbott did not testify during the trial in Snohomish County Superior Court, and the jury rejected the suggestion from his lawyers that he had sex with Van Cuylenborg but did not kill her or her boyfriend. It’s still unknown how Talbott encountered the pair and what happened during their final days.

“It’s been such a long wait for all of us,” John Van Cuylenborg, Tanya’s older brother, said after the verdict in a video posted by The Daily Herald newspaper. “It feels great to have some answers. We don’t have all the answers, but we have a lot more than we had for 31 years.”

When the couple didn’t return from their trip as scheduled, their families began a frantic search for them, including renting a plane to try to spot the copper-colored Ford van they had been driving.

About a week later, Van Cuylenborg’s body was found down an embankment in a rural area north of Seattle. She had been shot in the back of the head.

Hunters found Cook dead two days later in brush near a bridge over the Snoqualmie River — about 60 miles from where his girlfriend was discovered. He had been beaten with rocks and strangled with twine and two red dog collars, authorities said.

Talbott flinched and gasped when the jury read its verdict, then was pushed out of the courtroom in a wheelchair, the newspaper reported.

He is one of dozens of suspects authorities have arrested in old cases over the past year through the genetic genealogy, including a California man charged in the Golden State Killer case. The serial attacker killed 13 people and raped nearly 50 women during the 1970s and 1980s.

In Talbott’s case, a genetic genealogist used a DNA profile entered into the GEDmatch database to identify distant cousins of the suspect, build a family tree linking those cousins and figure out that the sample must have come from a male child of William and Patricia Talbott.

The couple had only one son: William Talbott II.

Once Talbott was identified as a suspect, investigators tailed him, saw him discard a coffee cup and then tested the DNA from the cup, confirming it matched evidence from the crime, prosecutor Justin Harleman told jurors during the trial.

“The use of GEDmatch — I hope more and more people will be willing to allow their DNA on these sites so that this world can be safer,” said Cook’s sister, Laura Baanstra.