DNA left on crime scenes and genetic information sent to an online genealogy service were instrumental to the capture of a suspected rapist and murderer.

The Golden State Killer eluded authorities for four decades, but the availability of new technology for analyzing evidence led to his arrest.

The Golden State Killer

The Golden State Killer is behind 12 murders and over 50 rape cases that occurred in the 1970s and 1980s. He also committed burglary. On Tuesday, authorities arrested 72-year old Joseph James DeAngelo after DNA evidence identified him as the Golden State Killer.

Building Genetic Profile From DNA Left At Crime Scenes

After Sacramento County District Attorney Anne Marie Schubert opened a cold case investigation of the Golden State Killer, investigators looked into the DNA samples left at the crime scenes that were still in storage. They used these to build a genetic profile of the suspected killer.

The DNA profile was then uploaded into the database of Florida-based DNA analysis firm GEDMatch. DeAngelo, a former police officer, did not send his DNA to GEDMatch but at least one of his distant relatives did.

People who are related share identical chunks of DNA and these shared DNA patterns can identify the relatives of an individual.

Using data from the DNA analysis company, investigators looked into online family trees that appear to mirror the DNA profile of the suspect. They also looked for clues about various individuals in those families to identify possible suspects.

DNA Evidence

The detectives thought that DeAngelo could be the person they were looking for due to several factors: his age, DNA and he lived in the vicinity where the crimes happened.

"We found a person that was the right age and lived in this area - and that was Mr. DeAngelo," said Steve Grippi, the assistant chief in the Sacramento district attorney's office.

The investigators then set up surveillance in the suburb where DeAngelo lived and collected his "abandoned" DNA samples. It was not clear what the investigators used, but there are a number of things such as a hairbrush or a soda can that may contain DeAngelo's hair, saliva, or blood.

Experts then compared the newly collected sample to the decades-old DNA taken from the crime scenes and found that this was a match to more than 10 of the murders. A second sample provided "astronomical evidence" that DeAngelo was indeed the Golden State Killer.

DeAngelo was arrested on Tuesday and now faces murder charges. He is expected to face additional charges.

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