The perils of expanding DNA searches to relatives

by jennifer mnookin

If you're convicted of a felony — or a misdemeanor in some states — your DNA goes into a database. That information helps primarily in the pursuit of repeat offenders. But some people want to extend the reach of that data to find people who are only a partial match.

It's a particularly personal form of a law enforcement fishing expedition. Called "familial searching," it targets not only the convicted, but their relatives as well. Sometimes, when an investigator tries to match a crime scene sample to the several million profiles in, say, the FBI's database, no exact match turns up. But there might be someone whose DNA profile is unusually similar.

If the partial match is sufficiently close, or if some of the genetic markers in the sample are sufficiently rare, it could mean that the crime scene sample was left by a close genetic relative of the person included in the DNA database. Thus, the familial search casts suspicion not on the convicted criminal in the database, but also on that person's siblings, parents or children.

Should forensic scientists reveal partial matches to police and prosecutors? Should officials be able to use this DNA to investigate relatives? Is this an encroachment on civil liberties?

There are no clear-cut answers. If we forgo partial matches, violent criminals may remain at large. Yet fairness and privacy concerns require that we should resist the impulse to engage in familial searching.

Until recently, the FBI refused to allow states to reveal partial matches in its database to other investigation agencies. But many prosecutors, including those in California, are lobbying hard to use the technique. A 2006 article in the journal Science argued that the use of kinship analysis could increase the number of cases that were solved by up to 40%.

Put plainly, such a practice would be discriminatory. If I have the bad luck to have a close relative who has been convicted of a violent crime, authorities could find me using familial search techniques. If my neighbor, who has the good fortune to lack felonious relatives, left a biological sample at a crime scene, the DNA database would not offer any useful information.

The concern about fairness is exacerbated because African Americans and Latinos make up an outsized portion of the DNA database compared with their proportion in the population at large. This means that African Americans and Latinos not in the database would be disproportionately available to familial searching. The same point could be made for the poor and working-class populations.

While we might not be sympathetic to the claim of a privacy violation made by a guilty person caught by familial search techniques, we ought to care that these procedures disproportionately affect the underprivileged.

If it is ethically and legally acceptable to use DNA search techniques on people without prior convictions, then why not have a national database that includes everyone? The misfortune of having a criminal in the family tree ought not to determine who's included in the database and who's left out.

Mnookin is a professor at the School of Law