EVERETT — For three decades, the families of Jay Cook and Tanya Van Cuylenborg had been left with only questions and fleeting memories.

On Friday morning, a long-awaited answer arrived.

A jury found William Talbott II guilty of two counts of aggravated murder in a trial that was the first of its kind.

Talbott did not testify. After the jury read its verdict, he flinched and gasped, then was pushed out of the courtroom in a wheelchair.

Judge Linda Krese set sentencing for July 24. There is only one possible sentence: life in prison.

The truck driver, 56, of SeaTac had been identified in a pioneering investigation led by the Snohomish County Sheriff’s Office.

A genealogist used a public DNA site, GEDMatch, to help build a family tree for the suspect based on DNA from a crime scene. Her research pointed to Talbott.

Since then, dozens of arrests have been made in cold-case crimes nationwide through a forensic method known as genetic genealogy, stirring a heated debate over police use of genetic databases.

Many suspects, including the former cop arrested in the Golden State Killer case, await a trial. This was the first case using the technique to go before a jury.

Other than semen at two crime scenes — including one in Skagit County — little else tied the defendant to the killings. His defense argued the semen came from a consensual act.

Talbott grew up seven miles from a third crime scene south of Monroe, where Cook had been bludgeoned with rocks, strangled with twine and left dead under a bridge.

Van Cuylenborg was found dead against a rusty culvert on Nov. 24, 1987, off Parson Creek Road in Skagit County. She was found almost a week after she and Cook went missing.

She was nude from the waist down. She’d been shot in the back of the head with a .380-caliber bullet.

Pheasant hunters stumbled upon Cook’s body on Thanksgiving Day under the High Bridge over the Snoqualmie River, south of Monroe.

A blue blanket covered his upper body. Investigators peeled it back to find he’d had been beaten around the head and strangled with twine tied onto two red dog collars.

Detectives had built a list of hundreds of potential suspects. Many were ruled out through DNA tests.

Semen had been found both on Van Cuylenborg’s body and in the van, on the hem of her pants. The sample was sent to Parabon NanoLabs, a private lab offering a new service to help police to build a rough digital sketch of a suspect’s face, through DNA.

Behind the scenes Parabon was working on another project, using public genealogy databases to identify suspects through their family ties. Quietly, the lab uploaded the genetic profile to GEDMatch.

By chance, second cousins on both sides of Talbott’s family had uploaded genetic profiles to the database.

A genealogist, CeCe Moore, traced the family lines to Talbott’s mother and father. They had daughters, but only one son.

The data report returned to the lab on a Friday in late April 2018. By that Monday, the genealogist had identified it belonged to Talbott.

Jurors listened to 1½ weeks of witness testimony: retired police officers who uncovered evidence in 1987; the bird hunter who found Cook’s body; the Bellingham bartender who gave Van Cuylenborg’s ID to the cops; the store clerks, the last people known to have seen the couple alive; and Snohomish County detective Jim Scharf, who fought tears on the witness stand as he recalled receiving word of a DNA match.

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