Interesting article on the back ground of how the investigators used his DNA to create a family tree beginning with his Great Great Great Grandparents and worked backwards.
"A lab converted the sample into a format that could be read by GEDmatch, which analyzes hundreds of thousands of DNA datapoints to determine relatedness. Holes waited anxiously as he fed in the killer’s profile.
Holes, prepared for another dead end, was heartened when the analysis returned. It wasn’t a close match, but the site found 10 to 20 distant relatives of the killer, roughly the equivalent of third cousins.
Holes knew that if he traced back the lineages of distant cousins far enough, he could find a common ancestor they shared with the killer. That turned out to be great-great-great grandparents from the early 1800s.
A daunting task lay ahead as Holes and his team began to trace offspring to the present day to find potential suspects. That meant filling in thousands of blanks.
“When you go that far back in time, you have trees that grow huge,” Holes said.
They used census data, old newspaper clippings and a gravesite locator to find the deceased relatives. When they got to the current day, they turned to police databases and websites such as LexisNexis.
Holes created his family trees using a tool on Ancestry.com. His team stole time on weekends and during meetings to plug the holes one by one. It was tedious work, and it wasn’t their full-time focus.
By April, they had pieced together about 25 distinct family trees from the great-great-great grandparents. There were roughly 1,000 family members just in the one that included DeAngelo.
The team began scouring the trees for potential suspects, men about the killer’s age who had connections to Sacramento and other locations of the crimes."
https://www.washingtonpost.com/loca...ory.html?noredirect=on&utm_term=.d23692aced0e