The three men who showed up at Michael Usry’s door last December were unfailingly polite. They told him they were cops investigating a hit-and-run that had occurred a few blocks away, near New Orleans City Park, and they invited Usry to accompany them to a police station so he could answer some questions. Certain that he hadn’t committed any crime, the 36-year-old filmmaker agreed to make the trip.
The situation got weird in the car. As they drove, the cops prodded Usry for details of a 1998 trip he’d taken to Rexburg, Idaho, where two of his sisters later attended college—a detail they’d gleaned by studying his Facebook page. “They were like, ‘We know high school kids do some crazy things—were you drinking? Did you meet anybody?’” Usry recalls. The grilling continued downtown until one of the three men—an FBI agent—told Usry he wanted to swab the inside of Usry’s cheek but wouldn’t explain his reason for doing so, though he emphasized that their warrant meant Usry could not refuse.
But the well-publicized success stories obscure the fact that familial DNA searches can generate more noise than signal. “Anyone who knows the science understands that there’s a high rate of false positives,” says Erin Murphy, a New York University law professor and the author of Inside the Cell: The Dark Side of Forensic DNA. The searches, after all, look for DNA profiles that are similar to the perpetrator’s but by no means identical, a scattershot approach that yields many fruitless leads, and for limited benefit. In the United Kingdom, a 2014 study found that just 17 percent of familial DNA searches “resulted in the identification of a relative of the true offender.”
The technology’s limitations have the potential to cause real harm: What if Michael Usry was not a filmmaker, for example, but rather a high school teacher whose alleged involvement in a girl’s murder was leaked to the media? Yet despite all that can go wrong, few states have developed guidelines. California, Colorado, Virginia, and Texas have detailed policies regarding how and when familial DNA searches can take place; Maryland and the District of Columbia explicitly forbid the technique. Elsewhere in the nation, cops are largely free to search as they see fit, which is why Idaho Falls police decided it was OK to sift through an Ancestry database of genetic data from thousands of people with no criminal records.
Familial DNA searching is only going to get more prevalent as the cost of rapid DNA analysis plummets and the size of genetic databases swells. States must start putting rules in place to protect citizens, beginning by prohibiting police from running searches through nongovernmental databases, as happened in Usry’s case. This is not only because of privacy concerns—the people who contribute their DNA to such endeavors, whether medical or genealogical, rarely expect to have their genetic code scrutinized by cops—but also because those databases haven’t been vetted for use by law enforcement. Police in Idaho Falls, for example, were able to obtain a warrant for Usry’s cheek cells because his father’s DNA “matched 34 of 35 alleles” of that of Angie Dodge’s killer. But how common are those particular alleles in the general population? Does this even mean that there is a familial link? This isn’t entirely clear. (Ancestry, which gave Idaho Falls police the name of Usry’s father in response to a court order, has since shut down the database in question because, the company said, the “site [had] been used for purposes other than that [for] which it was intended.”)