A 72-year-old man believed to be the Golden State Killer was found after cops trawled through an ancestry website to find his relations.

California cops have confirmed they used an ancestry DNA website to track down the man believed to be the Golden State Killer. The suspect, 72-year-old Joseph James DeAngelo, was arrested on Tuesday after police searched family tree after family tree on the ancestry website to find potential relatives.

The cops scoured through dozens and dozens of family trees in an attempt to find an “ancestor” of one of the website’s users who fit the DNA sample left at a previous crime scene. They filtered the "ancestors" to those around the same age as the killer and those who had lived in the same location.

When DeAngelo was arrested on Tuesday, police said it was a DNA sample that led to his arrest, confirming on Thursday the method they used in tracing his bloodline.

Read more: Patton Oswalt’s Irish American wife helped capture Golden State Killer

The suspected Golden State Killer is set to appear in court Friday. Authorities believe he was behind 12 murders and more than 50 rapes in the 1970s and 1980s. https://t.co/mixB9WAeIx pic.twitter.com/lNA4jFIf7M

— CNN (@CNN) April 27, 2018

Detectives eventually stumbled across the suspect’s name after finding one of his relatives. He fit the age range, had lived in the areas where the Golden State Killer murders took place and he was named as a suspect last Thursday. After six days of surveillance on his home, DeAngelo was taken into custody earlier this week.

Cops then confirmed the DNA match by taking a sample for his trash, resulting in a perfect match.

Joseph James DeAngelo is suspected of committing at least 12 killings and 50 rapes in 10 different counties across California between 1976 and 1986. He was charged with six counts of murder on his arrest.

Unfortunately, the Irish American crime writer Michelle McNamara who had worked so hard on gathering evidence, and penned the name "Golden State Killer," did not live to see his arrest. The 46-year-old wife of comedian Patton Oswalt died in 2016 after a determined investigation to reveal the identity of the killer.

McNamara's book, “I'll Be Gone in the Dark: One Woman's Obsessive Search for the Golden State Killer” was published in February.

Although local law enforcement have not credited McNamara with involvement they described the case as “a source of great frustration” and said McNamara and her blog posts on the case, on True Crime Diary, “kept interest and tips coming in but other than that there was no information extracted from that book that directly led to the apprehension.”

The suspect, 72-year-old Joseph James DeAngelo.