And it required the investigators who executed the arrest, filed the charges, and managed the six-county prosecutorial coordination that produced the June 2020 plea.
Michelle McNamara’s contribution was of a different kind but deserves acknowledgment: she brought the case to a new audience through her investigative writing, named it in a way that unified its previously fragmented public identity, and created public pressure for renewed investigative attention before her death in 2016. The book published posthumously from her work appeared in the same month as DeAngelo’s arrest, in a coincidence that its publisher could not have planned.
The Limits of the Method and What the Case Proves
It would be accurate to say that investigative genetic genealogy made a decisive difference in the Golden State Killer case. It would be inaccurate to conclude from that that the method will produce similar results in every cold case where investigators have preserved biological evidence.
The conditions that made the method work in this case were specific. The crime-scene biological evidence from the 1970s and 1980s had been preserved in sufficient quantity and quality to develop a DNA profile adequate for genealogy database searching — not a given for decades-old evidence. The genealogy database contained enough profiles, and the criminal’s family had enough members who had uploaded DNA, to produce useful matches. The genealogical research was feasible because the records needed to build the family trees — census data, birth certificates, marriage and death records — were accessible and adequate.
Cases where the biological evidence is too degraded, where the offender’s family has not participated in consumer genetic testing, or where the documentary records needed for genealogical work are incomplete or unavailable will not produce the same results. The method is powerful when its preconditions are met. When they are not, it cannot produce what it produced here.