Should Police Use DNA to Investigate a Suspect’s Family Members?

A shorter version of this was published in Nature Reviews Genetics [abstract].

In July 2010, California police used a new forensic technique called familial searching to capture the “Grim Sleeper,” a serial killer who had evaded them for a quarter century. With DNA obtained from a discarded pizza crust, investigators found in the state’s offender database not the profile of the killer himself but instead, through a partial genetic match, that of his son.  Based on the identification of a close genetic relative, a principal suspect was identified (1).

Forensic familial searching is practiced in some US jurisdictions and a number of other countries, and its use is increasing. Not surprisingly, this has raised significant scientific and social concerns. Careful consideration of these issues is especially urgent now, in light of the recent Supreme Court decision allowing the collection of DNA from arrestees prior to conviction (2,3).

How does familial searching work? In most forensic cases, investigators analyze DNA from a crime scene at 13 genetic markers determined by the federally managed Combined DNA Index System (CODIS) (4)...