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How Genealogy Tech Caught the Golden State Killer

a man wearing prison cloth being arrested | feature | How Genealogy Tech Caught the Golden State Killer
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On August 21, 2020, in a historical conclusion, a former police officer and “Golden State Killer,” Joseph DeAngelo, was given multiple consecutive life sentences without the possibility of parole. He committed over 120 burglaries, more than 50 rapes, and at least 13 murders spanning from 1973 to 1986. For decades DeAngelo got away with his crimes, but eventually, he was caught with the help of genealogy tech.

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Genealogy Tech Used in Landmark Criminal Investigation

a burglar is taking the purse a burglar is taking the purse | How Genealogy Tech Caught the Golden State Killer | Genealogy Tech Used in Landmark Criminal Investigation

When the Visalia Ransacker began his spate of burglaries in the 1970s, investigator Paul Holes was just a child. After graduating with a degree in biochemistry from UC Davis in 1990, Holes joined the police force and began working in the crime lab.

Shortly after he was hired as a deputy criminologist in 1994, his investigative curiosity got the better of him when he found an envelope marked “EAR.” The cold case investigator dusted off the crime files and began his secret obsession to find the East Area Rapist.

Holes was determined to find out who was responsible for the atrocities committed and would spend the next 14 years tracking down the perpetrator.

The evil-doer terrorized California for decades under the guise of “Visalia Ransacker”, “East Area Rapist”, and “Original Night Stalker”. It was only in 2001 that DNA evidence finally linked all the cases, and investigators discovered that they were the same person.

In 2013 true-crime author Michelle McNamara revived Holes’ quest to find “EARONS” (East Area Rapist Original Night Stalker), giving DeAngelo the moniker “Golden State Killer”. Sadly, McNamara died before the serial killer was identified, and her book, “I’ll Be Gone in the Dark”, was published posthumously in February 2018. Her work was later adapted into an HBO series of the same name.

Using the DNA evidence, investigators and McNamara pondered how they could use the data on trending genealogy websites like AncestryDNA and 23andMe, but hit a brick wall when the companies refused to hand personal information over to police. Also, the forensic data could not be sent to these companies because they required a large saliva tube.

What investigators could do was search the open-source genealogy website GEDmatch. Although less user-friendly, the database consists of exported raw data voluntarily given by customers who use other DNA testing services. GEDmatch also has more powerful matching tools that allow users to match one particular segment of DNA.

GEDmatch compares autosomal DNA, which is contained in the 22 pairs of chromosomes that don’t determine sex. Each person receives one set of chromosomes from each parent, and so the number of markers, known as single-nucleotide polymorphisms (SNPs), decreases by half after each generation.

Looking at several consecutive SNPs in common with other individuals, the genealogy tech uses algorithms to find a match in a nutshell.

Investigators uploaded the killer’s DNA from a Ventura County rape kit to the website and hoped for a close match, such as a cousin. Unfortunately, the data only revealed relatives the equivalent to third cousins – around 10-20 people with the same great-great-great-great-grandfather dating back to the 1800s.

Holes contacted genetic genealogist Barbara Rae-Venter, who built a genetic profile and mapped out about 25 family trees. Over the course of months, investigators slowly ruled out suspects by focusing on clues like sex, age, and place of residence when the crimes occurred. Of the 25, the family tree that linked the Golden State Killer contained over 1,000 people alone.

Investigators narrowed down the thousands of profiles to two suspects, one of which was ruled out by their relative’s DNA. This left DeAngelo as the main suspect.

DNA samples were collected from the door handle of DeAngelo’s car and tissue collected from his garbage, and he was arrested on April 18, 2020.

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Although these genealogy tech methods are encouraging for solving crimes, what are your thoughts on privacy matters for law-abiding citizens? Let us know in the comments section below.

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