Collection

The family-tree cases

Investigations reopened when crime-scene DNA was matched, through distant relatives, to a name.

By the 2010s, hundreds of thousands of people had uploaded their DNA to public genealogy databases to trace their ancestry. Investigators realized those family trees could be read in reverse: a profile built from crime-scene evidence, compared against the databases, points to cousins, and patient genealogy narrows millions of possibilities to a single household.

The 2018 arrest in the Golden State Killer case brought the method to public attention. The files here trace how it has since resolved cases that conventional DNA databases never could — several of them decades old, several in which the victim's family had waited a lifetime for a name.

The technique produces a lead, not a verdict. Every case here still proceeded to conventional evidence and the courts. What changed was that a cold trail suddenly had a direction.