Signaling a 'new era' in forensic investigation, a man caught through genetic genealogy gets life in prison for 1987 double murder

In a milestone for forensic criminal investigators, a convicted killer received two life sentences on Wednesday for a 1987 double slaying after becoming the first person arrested through genetic genealogy to be found guilty at trial.

“The conviction and sentencing of William Earl Talbott II marks a new era for the use genetic genealogy for identifying violent criminals since it has now been tested and tried in a court of law,” geneology expert CeCe Moore told ABC News.

William Earl Talbott II was arrested in May 2018 and charged with aggravated murder for the Washington state cold case killings of 20-year-old Jay Cook and 18-year-old Tanya Van Cuylenborg, authorities said. A jury found Talbott guilty last month.

"By Talbott not pleading guilty, he's put a whole new generation of people through his horror," one of Cook's sisters, Laura Baanstra, said in court Wednesday. "Thank God Talbott is finally off the streets."

The young victims, from Canada, were traveling to Seattle by van when they were killed.

On November 24, 1987, Van Cuylenborg's partially-clothed body was found in a ditch in a wooded area, authorities said.

Cook's body was discovered along a road two days later, authorities said.

Talbott led an "unremarkable life," one of Cook's sisters, Kelly Cook, said in court Wednesday.

The victims, "who essentially had everything to live for," Kelly Cook said, "would not have led unremarkable lives."

Decades went by without an arrest in the double slaying -- until Talbott was identified last year through genetic genealogy.

Genetic genealogy -- a novel technique that compares unknown DNA evidence to public genetic databases to identify suspects through their family members -- has been called a "game-changer" in the effort to crack cold cases.

In April 2018, the suspected "Golden State Killer" became the first public arrest through genetic genealogy. Since then about 70 suspects have been identified through the technology, according to Moore, who also appeared as an expert in ABC News "20/20" episodes.

While at least two men arrested through genetic genealogy have pleaded guilty in cold case killings, Talbott was the first of those arrested through genetic genealogy to stand trial, according to Moore.

Talbott was identified as a suspect when investigators took the unknown killer's DNA from the crime scene and uploaded it to a public genetic genealogy website. Promising matches were found for two of the unknown killer's relatives, authorities said, and once genealogists traced the suspect's family tree, they zeroed in on Talbott.

Investigators obtained a cup Talbott had used and tested the DNA, and found it matched the suspect DNA left at the crime scene, authorities said.

Talbott maintains his innocence, telling the court Wednesday, "I stand before you a man convicted of a crime that I did not commit."