How a genealogy site helped find the Golden State Killer — and what that means for the privacy of your genetic profile

Details are continuing to come out in the Golden State Killer case about how investigators found their suspect, Joseph James DeAngelo.

It was a familial DNA match with crime scene evidence that led officials to suspect the former police officer. Officials found that match by using the database from a genealogy website where people post their DNA data to get information about their ancestry.

Using a genealogy website in an investigation like this is really unusual, said John Roman, forensics expert and senior fellow at the research organization NORC at the University of Chicago.

The normal procedure for an investigation is to test crime scene DNA evidence, thought to belong to the perpetrator with FBI DNA databases to look for a match, and if a match is not found the case goes cold, Roman said.

The problem with using a website like this is that there's no protocol, Roman said. The privacy protections that are in place in the FBI database do not exist in this situation.

"In order to make these cases, we really need to understand what the protocols and processes are in ways that we know ensure privacy and keep the evidence of the case intact in a way that makes it useful," Roman said.

The privacy of the website users is a serious issue, Roman said, because DNA information is such a unique identifier of an individual. so now the question is whether the site users could have reasonably expected their DNA data to be used in an investigation like this.

The issue of how the DNA was obtained from the website could be something DeAngelo's defense brings up in court, Roman said, but he hopes the prosecution will have other evidence to support their case so that question won't cause a problem. 

"Everybody applauds the law enforcement diligence in this investigation and would really love to see it resolved," Roman said.