Is the NorCal Rapist Arrest Another Success Story for Forensic Genomic Genealogy?

On the morning of September 20, police arrested Roy Charles Waller, 58, of Benicia, California, for 10 rapes over a 15-year period starting in 1991. A Washington Post article described the crucial lead in the case as "what's called a familial DNA search." According to the Post,

    The arrest was reminiscent of that of Joseph James DeAngelo, who was arrested in April on the suspicion that he was the so-called “Golden State Killer,” who was wanted for raping dozens of women and killing at least 12 people in a bloody swath of crime that spanned decades in the state.
    Like DeAngelo, Waller was arrested after police searched the genealogy site GEDmatch for leads. In DeAngelo’s case, officials did what’s called a familial DNA search of GEDmatch, in which they sought to find someone who was closely genetically related to and worked backward to find a suspect. Familial DNA searching, particularly as it relates to government-run DNA databases, has come into wider use around the country, but it raises complicated questions about whether it means that the privacy rights of people are forfeited, in effect, by the decisions made by their relatives.
    It was not immediately clear if police did a familial search in Waller’s case or found his profile in GEDmatch.

In forensic genetics, "familial searching" normally refers to trawling a law-enforcement database of DNA profiles after failing to find a match between a profile in the database and a profile from a crime-scene sample at a mere 20 or so STRs (short tandem repeats of a short string of base pairs) in the genome of billions of base pairs. But a near miss to a profile in the database might be the result of kinship -- the database inhabitant does not match, but a very close relative outside the database does. A more precise description of such "familial searching" is outer-directed kinship trawling of law-enforcement databases (Kaye 2013).

The Post's suggestion that the NorCal Rapist may have been identified through "familial DNA searching" and the statement that "[f]amilial DNA searching, particularly as it relates to government-run DNA databases ... raises complicated questions about whether it means that the privacy rights of people are forfeited, in effect, by the decisions made by their relatives" is badly confused. The inhabitants, so to speak, of the law-enforcement databases, have not elected to be there. Their relatives, near or distant, have not chosen to enroll in the database. DNA profiles are in these databases because of a conviction or, sometimes, an arrest for certain crimes. The profiles are not useful for much of anything other than personal identification and kinship testing for close relatives (lineal and siblings).

The "genealogy site GEDmatch" is very different. It is populated by individuals who have elected to make their DNA searchable for kinship by other people who are looking for possible biological relatives. These trawls do not use the limited STR profiles developed for both inner- and outer-directed trawls of offender databases. They use the much more extensive set of SNPs (single-nucleotide polymorphisms) -- hundreds of  thousands of them -- that genetic testing companies such as 23-and-me provide to consumers who are curious about their traits and ancestry. Those data can be used to infer more attenuated kinship. Knowing that long, shared stretches of DNA in the crime-scene sample and the sample in a private (that is, nongovernmental) genealogy database such as GEDmatch could reflect a common ancestor several generations back enables genealogists using public information about families to walk up the family tree to a putative common ancestor and then down again to living relatives.

It is clear enough that California officials used the latter kind of kinship trawling in the publicly accessible genealogy database GEDmatch to find Mr. Waller. At a half-an-hour long press conference, Sacramento County  District Attorney Anne Marie Schubert refused to give direct answers to questions such as "Did a relative upload something?" and did you have to go through a lot of family members to get to him? However, she did state that "[t]he link was made through genetic genealogy through the use of GEDmatch." Eschewing details, she repeated "It's genetic genealogy, that's what I'll say." If Mr. Waller had put his own genome-wide scan on GEDmatch, why would Ms. Schubert add "a lot of kudos to the folks in our office ... that I call the experts in tree building"? The district attorney's desire not to say anything about specific family members reflects a commendable concern about unnecessarily divulging information about the family, but she could have been more transparent about the investigative procedure without revealing any particularly sensitive information on the family or any material that would interfere with the prosecution.

REFERENCES

• Eli Rosenberg, A Serial Rapist Eluded Police for Years. Then They Searched a Genealogy Site, Wash. Post, Sept. 22, 2018 (quorted above)
• Kristin Lam, “Real-life Boogieman” Who Raped Women Across California Arrested with Genealogy Site Data, USA Today, Sept. 21, 2018, 9:05 p.m. (Updated 4:58 a.m. ET Sept. 22, 2018).(a better account of the investigation)
• David H. Kaye, The Genealogy Detectives: A Constitutional Analysis of “Familial Searching”, 51 Am. Crim. L. Rev. 109 (2013) (proposing clearer terminology for discussing "familial searching" and kinship testing with and without databases)