DNA Q&A: Catching the Golden State Killer

DNA Q&A: Catching the Golden State Killer

In the 1970s and 80s a man known as the Golden State Killer terrorized California. Here's how some genetic genealogy sleuthing cracked this 35-year-old case.

In the 1970s and 80s, a man known by multiple names but eventually called the Golden State Killer terrorized California with robberies, multiple attacks on women and several murders. The last crime ascribed to this man occurred in 1986. Law enforcement used every known method to track him down, including DNA testing, but his case went cold.

At one point during those active years a forward-thinking Ventura county pathologist froze a DNA sample collected at a crime scene with the hope it would be useful in the future. That future has arrived.

On April 24, 2018, Joseph James DeAngelo was named as the leading suspect in this cold case. What was it that resurrected this case from the unsolved mysteries file? Citizen science. It is citizen science that determined in 2012 that they could band together and create a database independent of the genetic genealogy testing companies. The ticket into this database, called Gedmatch, is a data file. This file can be obtained from any genetic genealogy testing company. And, since it is just an Excel file, theoretically anyone can generate one and use it to query the database.

Read: How and Why to Download Raw Data from AncestryDNA

This is exactly what law enforcement did with the 35+ year old frozen sample that was sitting in the back of the freezer in Ventura County. Leading the effort was investigator and DNA expert Paul Holes who had spent years using the DNA collected from the Golden State Killer to query FBI and state databases, with no luck. There are two things that made the Gedmatch database more powerful than these other databases. First, it is the technology. The technology employed by the federal and state databases only allows you to identify individuals, or possibly very close family members. However, the testing completed by genetic genealogy communities and employed in Gedmatch allows you to find more distant relatives, like third and fourth cousins.

Secondly, Gedmatch contained what these previously databases did not: regular people. The only DNA in the state and federally run databases are those of previously convicted criminals, of which DeAngleo was not. It is through these regular people, that Holes and his team were able to identify DeAngelo as a suspect.

Holes was anxiously waiting at his computer when the results from Gedmatch first came in. Finding several third cousins, he and his team immediately set to work pursuing the genealogy of those matches, ultimately identifying a couple that were likely the great-great-great grandparents of the Golden State Killer. Four months of traditional genealogical research finally led them to two men who could have been in the right place at the right time to be perpetrator of these crimes. When additional DNA testing eliminated the first, Holes was left with DeAngelo. A discarded cup with DeAngelo’s DNA produced a match to the original sample collected at the crime scene, meaning that Holes and his team had enough evidence to arrest DeAngelo, and provide closure to a 45-year search for the man who ravaged California with his criminal escapades.