Genetic genealogy has been used for the first time in court to seal the fate of a killer who had been on the run for a 1987 double murder and may now be an accepted part of law enforcement investigations.

Tanya Van Cuylenborg, 18, and her 20-year-old boyfriend, Jay Cook, disappeared in November 1987 after leaving their home near Victoria, British Columbia, for what was supposed to be an overnight trip to Seattle.

Their bodies were found in separate locations, 75 miles apart and within two days of each other, in northwestern Washington state about a week later.

She had been shot and her boyfriend had been strangled but for decades, nothing else was known about the killings until police matched a DNA sample found on her body to one that had been entered on GEDMatch.

It gave a match to two second cousins of 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.

Police then tailed him and retrieved a coffee cup he had discarded, tested his sample against the one found at the crime scene and arrested him.

William Earl Talbott II has been convicted of the murders of a young couple in Washington state in 1987 after police matched semen left at the scene to the DNA profiles of his second cousins

Tanya Van Cuylenborg, 18, and her 20-year-old boyfriend, Jay Cook, disappeared in November 1987. Their bodies were found a week later. She had been shot and he had been strangled

He did not testify at the trial and why or how he killed the couple remains unclear but the case is the first ever to rely on genealogy testing.

While it has been used to identify killers in the past like the Golden State Killer, this is the first case in which a defendant has pleaded not guilty but been put behind bars because of the technology's results.

'There is no stopping genetic genealogy now.

'I think it will become a regular, accepted part of law enforcement investigations,' CeCe Moore, the genealogist whose work led to the arrest in the murder case, told The New York Times.

The victims' families welcomed the verdict.

'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.'

The young couple had gone on a road trip overnight to Seattle in their brown Ford van (shown) How they came to meet Talbott remains unknown. He did not testify

This is the scene where one of the bodies was found a week after the pair went missing

'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.

The victims's families said they knew something was wrong when they did not return from their trip as planned.

They began a search for them and rented 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.

Police matched his DNA to a male and female cousin and traced it back to their great grandparents to find him. He was the only son of the couple they believed had the closest match to the profile

William Earl Talbott II, did not deny that the DNA was his and argued instead that it did not mean he killed the pair - only that he had sex with Tanya

Lisa Collins, a forensic scientist, looks at a swab used to collect DNA from William Talbott II after they had traced him through the site

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.

Genetic genealogy was also used to catch the Golden State Killer suspect Joseph James DeAngelo

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.

He never denied that the DNA was his but argued that it did not prove he had had killed the pair, only that he had sex with Tanya.

The issue of whether or not genealogy websites should allow law enforcement to pillage their databases is a debated one.

Now, GEDMatch has changed its rules to inform users that when they submit their information, they are allowing it to be used for police investigations into rape and murder.

But over the last two years,there has been confusion and fear over how much they stick to those two categories.

It was used to make an arrest, for example, in the assault of an elderly woman in one case and in another, police claimed to be investigating a rape or murder but then charged the suspect the database produced with burglary.

Golden State Killer suspect, Joseph James DeAngelo - who is yet to go to trial -as arrested after his relatives submitted to it.