The case of Joseph James DeAngelo is now the best-known application of a method called investigative genetic genealogy, and it is sometimes described as though the technology identified him immediately and directly. That is not quite what happened. What the genealogy database provided was an entry point into a family structure that investigators did not yet have. What followed was investigative work: building family trees from public records, narrowing a large population of possible relatives to a smaller group of candidates, applying conventional investigative methods to corroborate the genetic lead, and eventually collecting biological material that provided the direct DNA comparison needed to move toward an arrest.
The headline is accurate. A distant relative’s DNA helped expose him. But “helped” is doing real work in that sentence, and the story of what it helped, and what it took before and after that help, is what this article is about.
The Crimes and the Communities They Changed
The first documented crime that investigators have attributed to DeAngelo occurred in Visalia, in Tulare County, in the spring of 1974. Visalia was a Central Valley city of roughly sixty thousand people at that time, a regional center surrounded by agricultural land, with the kind of stable working- and middle-class residential neighborhoods that expected nothing particularly remarkable from the weekly routines of its residents.
Beginning in March 1974, those neighborhoods experienced what would come to be called the Visalia Ransacker crimes. A burglar was entering homes in a specific pattern: targeting residential areas, entering at night, taking small and sometimes seemingly arbitrary items — coins, military memorabilia, personal jewelry, small cash amounts — while often ignoring valuables that would have been easier to sell. The pattern of the crimes was unusual enough to draw attention. Over approximately twenty months, the burglar is believed to have entered around 120 homes.