Author: Tina Hesman Saey / Source: Science News
GATHERING EVIDENCE
Using DNA to find a killer sounds easy: Upload some DNA to a database, get a match and — bingo — suspect found. But it took new genetic sleuthing tools to track down the man suspected of being the Golden State Killer.
Investigators have confirmed they used a public genealogy database, GEDmatch, to connect crime scene evidence to distant relatives of Joseph James DeAngelo. The 72-year-old former police officer, arrested April 24 at his home in Sacramento, is suspected in a string of about 50 rapes and 12 murders committed between 1974 and May 1986.
The news prompted a flurry of concerns about privacy and ethics — there’s no telling how many people in the public database are being subjected to what amounts to a “genetic stop and frisk,” says Alondra Nelson, a sociologist at Columbia University. But others say they doubt police are actively trolling genealogy websites for suspects. Too many resources are required to do this sort of work, says Sara Katsanis, a genetics policy scholar at Duke University’s Initiative for Science & Society. “I don’t think this is going to become commonplace.”
Police haven’t yet publicly detailed the methods that led them to DeAngelo. Yet DNA experts say the simple upload-and-match scenario wouldn’t have worked in this case. DeAngelo’s DNA wasn’t in any police database. And snippets collected from crime scenes aren’t in the same form as the DNA in genealogy sites. In addition, consumer testing companies don’t participate in criminal investigations without a warrant. Even if a company was willing to help, police didn’t have saliva or cheek swabs from potential suspects the companies need to conduct their tests. So investigators would have had to do a lot of genetic legwork to get the DNA data and format it in a way that GEDmatch could recognize.
Colleen Fitzpatrick and Margaret Press have pioneered a way to do just that. The pair cofounded the DNA Doe Project, a nonprofit that uses genetics and genealogy to put a name to remains from unidentified people, including crime victims. The techniques developed for their organization are probably the same ones used in the Golden State Killer case, Fitzpatrick and Press say.
Forensic DNA fingerprints in law enforcement databases are composed of 20 “short tandem repeats.” Those are places in the human genetic instruction book — the genome — where a string of two to six DNA bases, or letters, repeat. For instance, ACGTACGTACGT would be three repeats. People have varying numbers of repeats at these locations. Police have used “familial searches” of law enforcement databases with short tandem repeats to identify suspects in some cases, but that approach has led to wrongful accusations in others.
Short tandem repeats, or STRs, are not the sort of DNA data found in GEDmatch. That database is a repository where people can voluntarily upload raw genetic data generated by consumer testing companies, such as 23andMe, Ancestry, Family Tree and others. So GEDmatch allows people to find relatives…
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