California Killer Caught by DNA

How technology captured the elusive murderer

Kimi Andrew
The Santa Clara
January 17, 2019

Ancestry websites are a new phenomenon, with millions of people uploading their DNA online to learn about their heritage. But in April 2018, an ancestry website did more than just tell someone their country of origin—it helped law enforcement catch a murderer.

On Monday, Jan. 14, Barbara Rae-Venter, a forensic genealogist; Kelley Kulick, Deputy Public Defender for Santa Clara County and James Gibbons-Shapiro, Santa Clara County Assistant District Attorney held a discussion in Lucas Hall about the science behind catching the Golden State Killer.

The Golden State Killer was a murderer, rapist and burglar who took the lives of at least 13 victims and committed more than 50 rapes in California between 1974 and 1986.

The well-known killer was thought to have gotten away with his crimes for over 40 years—until new science and a lucky break brought law enforcement to Joseph James DeAngelo, the suspected Golden State Killer.

At Monday’s talk, Rae-Venter discussed her time working with law enforcement on the Golden State Killer case and explained exactly how DNA was used to catch DeAngelo.

Following DeAngelo’s arrest, some people incorrectly thought that information was taken from websites like Ancestry.com in order to find a familial match to DeAngelo.

Rae-Venter explained that, in reality, a public data collection website called GEDmatch was used to find the killer.

This website is geared toward users who have already submitted their DNA to an ancestry website like Ancestry.com or 23andMe.

Users are able to take the data they have received back from the ancestry website and upload it to GEDmatch.

When uploading data to GEDmatch, users agree to make their data public in order to match them with potential relatives who also have used the website.

It was through GEDmatch that law enforcement officials were able to finally uncover the Golden State Killer’s identity.

Law enforcement, along with the help of forensic genealogists like Rae-Venter, came up with the idea to upload DNA found at one of the Golden State Killer’s crime scenes—DNA they believed belonged to the perpetrator.

Eventually, a GEDmatch user’s DNA turned out to be a sixth-cousin match to the Golden State Killer.

Through this match of public data on GEDmatch, law enforcement then was able to catch DeAngelo.

Rae-Venter also discussed the merits and possible drawbacks of using DNA websites like GEDmatch to catch criminals.

One issue is the prevalence of contaminated DNA.

Kulick, a public defender, explained that crime scenes can be messy and it’s always possible the DNA pulled from a scene can be “discarded DNA,” or DNA transferred from one person to the killer—through something as simple as a handshake—which the killer then leaves at the crime scene.

Kulick said law enforcement officials are able to pick up smaller pieces of DNA more than ever before thanks to rapidly advancing technology.

DNA can be as miniscule as a skin cell left on the murder weapon.

This skin cell could easily be discarded DNA, Kulick explained, and could be from someone who was never at the scene of the murder.

The public is also hesitant about encouraging the use of DNA testing websites to find criminals because some think it’s an invasion of privacy.

But when polls are taken to see how comfortable people are with using DNA websites in police cases, Rae-Venter explained that people are comfortable with the new technology when it comes to catching a violent criminal— someone who has committed murder or sexual assault.

Contact Kimi Andrew at kandrew@scu.edu or call (408) 554-4852.