Last week, California police arrested Joseph James DeAngelo, the man suspected of being the “Golden State Killer” or “East Area Rapist”, a serial killer and rapist who terrorised parts of California in the 1970s and 80s.

Of particular interest is how he came to be arrested, with the help of DNA matched on a genealogy website.

With the development of DNA technology in the 1980s and 90s, police determined that forensic samples collected from the killer’s crime scenes pointed to a single perpetrator. However, they had no DNA match in their database. So, investigators began comparing DNA samples with online sources.

GEDmatch.com is an “open source” database that allows users to share their genetic profiles generated by sending DNA samples to larger commercial sites like ancestry.com. It holds genetic information of about 800,000 users.

California state police created an “undercover profile” and uploaded the killer’s DNA profile to the website. They found a match – a distant cousin of DeAngelo had uploaded his own DNA profile to  map his family tree.

DeAngelo is a former police officer, and had never been a suspect before the DNA match led police to him. Prior to his arrest, police surveilling him also conducted further DNA tests on items he had left in public places.

GEDmatch’s policy advises users that their information will be shared with other users. Though they do not share information with third parties, users are warned DNA information could be used for purposes other than genealogical research. The website also allows use of aliases. Nevertheless, users must check a box acknowledging they are uploading their own DNA samples, are authorised to do so or are the sample owner’s legal guardian.

The case has raised concerns regarding privacy and the ethics of using personally identifiable information. Whilst it has potentially solved this case, allowing police to “data match” in this way, and the possibility of being connected to a crime because a distant relative posted their DNA online without your knowledge or consent, could have major privacy ramifications. It will be interesting to see whether people continue to upload DNA profiles online!