Law enforcement investigators have recently begun to solve old cold cases by tracking down criminals via their relatives’ DNA. From the New York Times:

Most White Americans’ DNA Can Be Identified Through Genealogy Databases

Only two percent of the population needs to have done a DNA test to identify nearly everyone else, researchers found.

By Heather Murphy

Oct. 11, 2018

… Already, 60 percent of Americans of Northern European descent — the primary group using these sites — can be identified through such databases whether or not they’ve joined one themselves, according to a study published today in the journal Science.

Within two or three years, 90 percent of Americans of European descent will be identifiable from their DNA, researchers found. The science-fiction future, in which everyone is known whether or not they want to be, is nigh.

The science involves a search for third cousins. To identify a person through a DNA sample, an investigator uploads a previously analyzed genetic sequence to a database. The goal is to find someone who shares enough DNA to place them in the third cousin or closer range. Most of us have at least 800 people out there, somewhere in the world, who fall into this category.