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Cutting-edge DNA analysis is opening new investigative avenues for police, including sheriffs in Washington State who have been looking into the 30-year-old murders of a young couple from British Columbia.

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Tanya Van Cuylenborg.HO - Snohomish County Sheriff's Office/The Canadian Press

The Snohomish County Sheriff’s Office has called a news conference for Wednesday in Everett, Wash., to discuss the murders of 18-year-old Tanya Van Cuylenborg and 20-year-old Jay Cook, both from the Victoria-area.

No arrests have ever been made in the murders of the high-school sweethearts, who vanished on a trip to the Seattle area in late 1987.

Their bodies were found a few weeks later in separate locations in Washington State. Mr. Cook had been strangled while Ms. Van Cuylenborg had been sexually assaulted and shot.

On Wednesday, investigators say they will unveil what the sheriff’s office describes as new suspect information produced from a groundbreaking method of analyzing DNA.

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Jay Cook.HO - Snohomish County Sheriff's Office/The Canadian Press

“What it is, really, is just an entirely new way to think about forensic DNA,” said Ellen Greytak, director of bioinformatics at Parabon NanoLabs, which used Snapshot DNA phenotyping to help the Snohomish County Sheriff’s Office on the cold case.

Ms. Greytak could not comment on the specific investigation, but explained that DNA phenotyping looks at pieces of DNA code to predict a person’s appearance, including their eye, skin and hair colour, facial features and ancestry.

“Traditionally, DNA found at a crime scene is treated like a fingerprint, so you can use it to match that DNA to a database or to a suspect you’ve already identified. But if it doesn’t match either of those places, that DNA can’t tell you anything more,” she said.

This method treats the sample as a blueprint instead, Ms. Greytak said.

“It actually contains all the information that made that person and so if we can look at the person’s DNA and code for eye colour, face shape or ancestry, we can predict information about that person and give the investigators something they didn’t have before.”

It allows DNA to be used as a “genetic witness” when there may not be a human witness, Ms. Greytak said.

“What this can do is provide a description of that person, objectively, just using the DNA and give them that information to go on that they didn’t have before,” she said.

The technology isn’t for individual identification, Ms. Greytak added, and there are traits it can’t predict, including age and body weight, so the company creates profiles of a young adult that can then be adjusted.

Their predictions can help police narrow down their suspect list and save time in an investigation, she said.

“We work on so many cases where, when we give the investigators our predictions, they say, ‘Oh my gosh. We’ve been looking for someone completely different.’ ”

Ms. Greytak said the technology has been used in more than 150 cases around the world since it became commercially available in 2014.

Typically, the samples are blood or semen collected at a crime scene, but Ms. Greytak said they have also taken DNA from bones to create profiles of unidentified remains.

Police in Washington State have revisited the Cook and Van Cuylenborg case several times, and even opened their files to FBI profilers and homicide experts in Britain.

It took police 23 years to find the Canadian man they said wrote the families taunting letters about their children. The man claimed he killed the couple and bragged he would never be caught. Police later determined he was mentally ill and not a suspect in the deaths.

At the time of the murders, police said the killer abandoned the van the couple was driving in a Bellingham, Wash., parking lot.

Skagit County sheriff’s Detective Tobin Meyer said in 2010 that the killer came prepared with a kit, likely containing a gun, zip ties, gloves and other tools.

Police believe the suspect picked the couple at random, likely crossing paths with them in downtown Seattle.

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