Lonnie Franklin, Jr., who is currently on trial for allegedly being the serial killer known as the Grim Sleeper, was linked to the murders by the Los Angeles Police Department through a familial DNA search. Back in 2010, Franklin's son, Christopher, had been convicted of a weapons charge and an analysis of his DNA sample threw up a red flag because of its similarity to the wanted serial killer's, leading officers to investigate the family.
A new study in PLOS One indicates that more distant relatives, such as half-siblings, first cousins, half-first cousins, and second cousins, could be incorrectly identified through such a familial process as first-degree relatives.
Researchers from University of California, Berkeley, and New York University conducted a simulated computer search — adhering to the policies California has set forth for familial searches — of randomly generated DNA profiles of related and unrelated people. The search was based on 13-locus CODIS genotypes and YFiler Y-chromosome haplotypes, and the generated DNA profiles were from people of five different ethnic backgrounds.
"[The] protocol has the advantage of returning few spurious leads — if a lead is generated, it is almost certainly a relative of the crime scene sample source," the researchers note. "Our findings, however, suggest that the closeness of the lead to the source is an open question." They report that there is between a 3 percent and 18 percent chance that a first cousin will be identified as a full sibling.
First author Rori Rohlfs from Berkeley tells LiveScience that police may then decide to investigate extended families, whose members might not even know the suspect. Further, she notes that this will disproportionately affect minority families as databases contain more DNA samples from minorities.