The challenge in the Lori Ruff case was that Lori herself was dead. There was no DNA sample from her directly. But there was a source of DNA that could be used to reconstruct her profile.
—
## The Phasing Method
Lori Ruff’s daughter had been born in September 2008. She was, at the time Fitzpatrick began working on the case, a small child. Her DNA, however, contained half of her mother’s genetic material — the half that she had inherited from Lori rather than from Blake.
Blake Ruff cooperated with the investigation. He and his daughter submitted DNA samples through a direct-to-consumer testing service, sending saliva samples to both Ancestry.com and 23andMe. Fitzpatrick then applied a technique called phasing.
Phasing, in this context, is a method of separating the DNA inherited from each parent. Because the daughter’s genome is composed of equal contributions from her mother and her father, and because Blake’s DNA profile was known, it was possible to subtract Blake’s genetic contribution from the daughter’s profile, leaving behind a reconstruction of the mother’s DNA. The result was not identical to having a direct sample from Lori, but it was a workable approximation — sufficient to search the databases for relatives.
The search produced matches. There were individuals in the databases who shared segments of DNA with the reconstructed maternal profile in quantities consistent with the relationship of a cousin. These were not close relatives who would obviously know who Kimberly McLean was; they were distant relatives, third cousins and fourth cousins, people who shared a great-great-grandparent or great-great-great-grandparent with the woman who had become Lori Ruff.