Familial DNA searching

Familial DNA searching is an investigative method for using an unknown offender’s DNA to identify a possible relative in a database, rather than finding the offender through a direct profile match. In the Golden State Killer investigation, it represented a potential way to turn the offender’s genetic trace into a lead about his family—but its reach depended on who was represented in the databases available to law enforcement.

Method and Investigative Promise

The book presents the killer’s DNA as the investigation’s strongest asset, while emphasizing that a profile can only be compared with the records available to search. A familial search might produce an alert if a close male relative—such as the offender’s father, brother, or uncle—had a qualifying record. Investigators could then examine that relative’s family and focus on a member whose history or location fit the crimes. The method therefore offers an indirect path: a database hit on a relative can create an investigative lead, but it does not itself identify the offender.

Database Limits

The Golden State Killer’s DNA had not matched a record in CODIS or in California’s penal-system Y-STR database. The book explains that California was one of only nine states permitting familial DNA testing within its state database, but that database contained people convicted of crimes. In the scenario described, a qualifying relative’s felony conviction during the preceding sixteen years could have generated an alert for Paul Holes or Erika Hutchcraft, allowing investigators to investigate the relative’s family. Without a qualifying relative in the database, the approach could yield no lead, regardless of the profile’s value. The absence of a match therefore reflected a limit of database coverage, not the absence of usable DNA evidence.

Commercial Genealogy as a Separate Route

The book distinguishes government familial searching from the possibility of searching public or commercial genealogy databases. Michelle considered entering the killer’s Y-STR markers into an online genealogy resource; she thought a result might point toward a surname or shared ancestor. But that was not equivalent to obtaining a familial-search hit from a law-enforcement database. The commercial approach raised a practical obstacle: the available evidence was a DNA profile on paper, not the killer’s saliva or a swab that could be submitted in the ordinary way. A scientist friend of Billy’s reportedly knew of a possible workaround, but the prospect also raised questions about companies’ terms of service, privacy, and the Fourth Amendment to the United States Constitution. The book presents those concerns as a tension around the method, not as a settled legal answer.

Role in the Investigation

Familial DNA searching belongs to a wider effort to make genetic evidence useful when direct comparisons fail. The earlier testing of three stored glass tubes in October and November 1996 shows another route by which DNA evidence advanced the investigation: those tests produced results that Orange County investigators planned to share with families, though Roger Harrington had died before the calls were made. Familial searching addressed a different problem—how to proceed when the offender’s profile had no direct database match. Its promise lay in converting a missing match into a possible family connection; its constraints lay in database eligibility, coverage, and the rules governing access to genetic information.