Page 73 of Fire and Bones
I was able to read Thacker now. Knew that behind the blank look her mind was already searching for a path toward additional free expertise.
“What do you know about forensic genetic genealogy?” I asked.
“It’s pricey as hell.”
“And?”
“The cops in Colorado used it to nail the Golden State Killer.”
“In California, actually.”
“Isn’t Golden a town in Colorado?” Thacker asked.
“Yes, but the killer preyed on victims across California.” I was growing impatient. “Do you know how genetic genealogy works?”
“I do. But something tells me I’m about to learn more.”
“Condensed version. An investigator collects a biological sample—blood, semen, hair, skin. That sample contains DNA that can be read through genetic sequencing.”
“Might contain DNA.”
I acknowledge Thacker’s point with the lift of one hand. “Are you familiar with how that sequencing is done?”
“I am,” Thacker said. “And I know that once a genetic profile is created, that sequence is added to a public database of DNA sequences on a website like GEDmatch.”
“A database containing genetic profiles uploaded by consumers who’ve purchased DNA tests.”
Thacker had decided to keep playing along. “Yes, kits sold by companies like 23andMe or Ancestry. Why do people do that?”
Though probably a rhetorical question, I answered anyway.
“Maybe they’re curious about possible genetic predisposition to disease. Maybe they want to find relatives in Zimbabwe. Their motives aren’t the point. As you know, cops and coroners do it because they’re interested in whether an unknown body or perp, an unsub, is related to other people in the database.”
“Sure. Potential relatives are determined by the number of shared genetic variants. But how often does a user actually find a close relative?”
“Rarely,” I conceded. “Unless the user comes from a family whose members are all bonkers about genealogy. Usually what they find are third cousins or further out. That’s where traditional genealogy comes into play.”
Thacker nodded. “Tracking down records like birth, death, and marriage certificates, census data, obituaries, social media, etcetera. That data is then combined with the DNA data to build a family tree of individuals who might be related to the ‘unsub,’ as you term him or her. Then investigators use conventional methods like physical descriptions, eyewitness statements, timelines, to narrow the field. I don’t live in a cave, Tempe.”
“I never thought you did.”
“You’d like me to try to ID your subcellar vic using forensic genetic genealogy?”
“Yes.”
“No can do.”
“Why not?”
“Let’s loop back to my opening line.”
It took me a moment.
“It’s expensive?” I said.
“Far too expensive, given my budget. Do you know how many bodies I have in my coolers right now?”
“I don’t.”