Fourth Amendment to the United States Constitution

The Fourth Amendment to the United States Constitution is presented as one of the legal barriers to using commercial genetic genealogy databases in the search for the Golden State Killer. The book does not set out the amendment’s doctrine or resolve how it would apply; instead, it places the constitutional concern alongside privacy policies, company terms of service, and the investigative possibilities opened by DNA technology. Its significance lies in the gap between a potentially useful investigative method and the contested authority to use it.

Public DNA Systems and Their Legal Framework

The book contrasts commercial genealogy services with the public forensic system. The DNA Identification Act of 1994 established the FBI’s authority to maintain a national database, CODIS. In the described system, local crime laboratories submit unknown crime-scene samples and certain collected suspect samples to state databases; the state systems verify and compare them before forwarding eligible profiles to CODIS. California samples are automatically uploaded to the state system every Tuesday, and states also collect DNA from jails and courthouses. This established channel for forensic comparison is distinct from the commercial databases Michelle McNamara hoped investigators could search.

That public infrastructure developed alongside major changes in laboratory capability. When the Orange County Crime Lab began incorporating DNA testing in the early 1990s, processing a case could take up to four weeks, and the sample needed to be relatively large and well preserved. The earlier RFLP profiling process was laborious. By contrast, the book describes contemporary testing as capable of producing a genetic fingerprint from a small number of skin cells within hours. The changing scale and speed of analysis made more investigative uses imaginable, but did not by itself answer who could lawfully access which databases.

Commercial Genealogy and the Constitutional Concern

The commercial services offered a different kind of possible lead. The book gives 23andMe and Ancestry.com profile totals of 1.5 million and 2.5 million, respectively, and explains that a crime-scene profile might point investigators toward a perpetrator through a cousin in one of those databases. Neither company would work with law enforcement, citing privacy issues and their terms of service. The narrative identifies privacy and illegal-search-and-seizure concerns as part of the locked door facing this proposed approach, naming the Fourth Amendment without claiming to settle its legal application.

Michelle McNamara wanted investigators to be able to enter the killer’s DNA into those growing commercial databases. She had a profile on paper, not the killer’s saliva or a swab, and the companies’ normal process required a customer to submit a saliva sample in a tube. A scientist friend of Billy Jensen’s suggested that there might be a way around that practical obstacle. The book frames the possibility alongside the question of whether technical feasibility should determine investigative practice; it does not report that Michelle or investigators carried out such a search.

Limits, Stakes, and the Unresolved Question

The Fourth Amendment therefore functions in the account not as a fully explained rule but as a limit that cannot be ignored when investigators consider repurposing privately held genetic information. The proposal raised distinct questions: whether a database could produce a useful family lead, whether access would comply with company policies, and whether the method would be compatible with privacy and constitutional protections. The narrative keeps those questions separate from the scientific possibility of matching or tracing DNA.

That distinction gives the legal concern force. Public databases had statutory authority and defined submission pathways, while commercial databases were governed by company terms and privacy positions that barred cooperation with law enforcement. The book leaves the conflict open: the potential investigative value of a vast genetic resource did not itself confer permission to use it. The Fourth Amendment marks one edge of that unresolved boundary, alongside the private rules and choices that determine whether such information is available at all.