Joseph James DeAngelo, 72, was arrested on Tuesday and charged with the murder of Katie and Brian Maggiore in Sacramento County in 1978.
On Thursday, FBI agents and police raided the DeAngelo house in Citrus Heights, a city about 16 miles northeast of the Californian capital.
Three days after DeAngelo's arrest, more detail emerges on what led the authorities to believe he was behind the 12 murders and more than 50 rapes in the 1970s and 1980s.
Authorities Finding a Suspect By Comparing Genetic Profiles to Genealogies According to the Sacramento District Attorney
public prosecutor, the police collected the DNA of a crime scene containing genetic material from a relative registered on genealogical sites, said Deputy District Attorney Steve Grippi
While it is unclear which DNA service was used, four companies contacted by CNN denied being in contact with the case.
Ancestry, Vitagune, MyHeritage, and 23andMe said they did not provide customer information to the law enforcement officers  Businesses allow their customers to run a test at home and submit their DNA. The scientists then compare the DNA with those they have already recorded, hoping to connect them to unknown branches of their family tree.
Suspect was a reclusive neighbor
DeAngelo – the man accused of being the Golden State killer – is a former police officer, a Vietnam veteran and a mechanic.
He served on board the USS Canberra, a guided missile cruiser, during the Vietnam War, according to Navy Public Affairs.
In the early 1970s DeAngelo worked as a police officer in Exeter and Auburn. The authorities said some of the alleged crimes of the Golden State killer had overlapped DeAngelo's time as a police officer.
"Most likely he committed these crimes in the time he was employed as a peace officer, and obviously we will investigate if it was actually in the workplace," said Sheriff Scott Jones of Sacramento.
DeAngelo was fired from his law enforcement job in 1979 for stealing a can of dog repellent and a gavel from a drugstore.
He continued to live what seems to be a quiet life. He worked for 27 years as a mechanic in the distribution center of a supermarket chain in Modesto, until he retired last year, said a spokeswoman for the company.
DeAngelo had at least three daughters, according to Kevin Tapia, who has lived near the suspect for 20 years.
Neighbors have said that DeAngelo was largely kept to himself and sometimes shouted at people who came too close to his fence, but said he had become a hermit in recent years.
DNA role in the investigation
 Bruce Harrington has constantly urged California officials to use DNA tests, in the hope that they will kill the man who killed his brother and sister-in-law nearly 40 years ago could catch.
Many elected officials and human rights groups voted against any attempt by Harrington and the state wished to extend the California DNA database for offenders.
Critics called the privacy of persons in police custody and questioned the constitutionality of allowing the state to collect DNA samples without evidence of guilt.
Harrington spent years before the Public Security Committees until California voters hit Proposition 69, known as the "DNA Fingerprint, Unsolved Crime and Innocence Protection Act "adopted in 2004.
The proposal gave the state broader powers to collect DNA. Now it could get samples of anyone who was not only convicted for a crime, but even arrested for one.
In some cases, the authorities were also able to collect DNA from arrests.
The use of DNA technology in DeAngelo's arrest highlights the progress that law enforcement agencies in California have made in their use of forensic science.
"I started my search in the mid-'90s, it was fifteen years before we heard that a DNA sample was taken from our scene," said Harrington
CNN's Cheri Mossburg, Stephanie Becker , Rosalina Nieves and Ray Sanchez contributed to this report.