In 2013, Chelsea Rustad was 31 years old and realized she could not name a single one of her great-grandparents. As she told “48 Hours” correspondent Erin Moriarty, “It’s not that far back, right? But I couldn’t name them.”

So Rustad, a resident of Tumwater, Washington, went online to build her family tree. She learned her roots stretched from Washington State through North Dakota and back to Norway. She found new relatives and connected with them on social media. But it was a second cousin she never spoken to who turned out to be the one who would change her life forever. And it was a Halloween photo from when she was just 5 years old that set the whole process in motion.

“Whenever there’s a branch of the tree that I — or an individual that there’s very little info on … I’m kind of extra curious about that person, you know. Like … why is there nothing on them?” she said. When she started her search, Rustad had found a family of second cousins from Snohomish County — the Talbotts. Rustad was able to connect and exchange messages with the sisters, but their brother, William Earl Talbott II, was all but invisible.

“The most striking thing about him would be his absence. He doesn’t have a social media presence. No Facebook. No Instagram. No Twitter. No YouTube,” Rustad told Moriarty in “A Killer in the Family Tree.”  “Usually, people have some type of internet presence … and there was nothing for him. I thought that was…