Abstract
Consumer genetics databases hold dense genotypes of millions of people, and the number is growing quickly. In 2018, law enforcement agencies began using such databases to identify anonymous DNA via long-range familial searches. We show that this technique is far more powerful if combined with a genealogical database of the type collected by online ancestry services. We present a "genealogical triangulation" algorithm and study its effectiveness on simulated datasets. We show that for over 50% of targets, their anonymous DNA can be identified (matched to the correct individual or same-sex sibling) when the genetic database includes just 1% of the population. We also show the effectiveness of "snowball identification" in which a successful identification adds to the genetic genealogical database, increasing the identification accuracy for future instances. We discuss our technique's potential to enhance law enforcement capabilities as well as its privacy risks.
