More than 30 years after his last known attack, the police finally tracked down the Golden State Killer. But how did they find Joseph James DeAngelo, the man who pleaded guilty to numerous crimes on Monday, June 29? The investigation relied on modern science and technological developments like familial DNA searches in order to find their prime suspect.

According to the Los Angeles Times, investigators were able to link DNA evidence from one of the crime scenes to one of DeAngelo’s distant relatives who used a genealogical database similar to Ancestry.com. The website lets users upload their DNA profile for free to build their family tree — but, since it doesn’t require users to buy and take a DNA testing kit, law enforcement officials were able to upload the Golden State Killer’s DNA profile without submitting an actual DNA sample. They could then connect that to a familial match.

Joseph James DeAngelo Pleading Guilty in Court
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From there, police were able to trace the family tree until they found a family member similar to their criminal profile. Once they identified Joseph James DeAngelo as a suspect, they obtained his DNA in order to compare the samples from a crime scene. ABC reports they first linked him to DNA taken from his car door handle and later conclusively linked him to the crimes with a tissue taken from his trash.

CNN states DeAngelo was arrested in April 2018 and later faced 13 counts of “first-degree murder and special circumstances (including murder committed during burglaries and rapes)” as well as 13 counts of kidnapping. Though his crimes spanned six counties, including Santa Barbara and Contra Costa, California, his trial took place in Sacramento. On June 29, he pleaded guilty to all of the charges — and informally confessed to several more crimes as part of his plea deal.

Joseph James DeAngelo in Court
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Taking a plea allowed DeAngelo to avoid the death penalty and avoid additional charges from counties where he was not yet on trial. Because of his plea, he’ll instead face 11 consecutive life sentences without the possibility of parole as well as 15 concurrent life sentences. That doesn’t take into account the additional time he’ll get for weapons charges. DeAngelo also agreed to waive his right to appeal his conviction.

The Golden State Killer case is currently being chronicled in the docuseries I’ll be Gone In the Dark, which is based on the investigative book written by the late true crime author Michelle McNamara. You can check it out on HBO on Sundays.

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