The method that Colleen Fitzpatrick applied to the Lori Ruff case — reconstructing the subject’s DNA from a child’s profile, then using that reconstruction to search for relatives in consumer genealogy databases — was at the leading edge of what is now an established investigative field.
Forensic genetic genealogy, sometimes called investigative genetic genealogy, uses the large databases that direct-to-consumer genetic testing companies have accumulated to search for relatives of unknown individuals. It is a field that has developed rapidly since the mid-2010s and achieved widespread public attention with the 2018 identification of the Golden State Killer, Joseph James DeAngelo, who was identified through a search of the GEDmatch database using DNA from crime scenes.
The Lori Ruff case predated that high-profile application and represents an early use of the method in an unusual context: not a homicide investigation using crime scene DNA, but an identification case using DNA reconstructed from a family member. The challenge Fitzpatrick faced — working from an indirect sample, using phasing to reconstruct the maternal profile — required adaptations of the basic method that were not yet standard practice.
The principles underlying the method are not mysterious. DNA is passed from parents to children, and segments of DNA are shared among relatives in predictable quantities. A third cousin shares approximately one percent of your DNA, on average. That one percent is distributed across the genome in segments that, with modern analysis of hundreds of thousands of genetic positions, can be identified and used to establish that a relationship exists. The genealogical research that follows a DNA match identification is traditional in method — searching public records, building family trees, tracing lineages forward and backward through time — but it is guided by the genetic signal in a way that unfocused genealogical research cannot be.