The technique used by police to catch the man they claim is the infamous Golden State Killer could have chilling consequences for users of a growing kind of website.
In recent days, investigators have revealed how they used an ancestry website to find a man they say is the man who tortured, raped and killed numerous people over a long period in California. They have described the technique as groundbreaking, and detailed how it relied on the latest technology and data.
But many say the technique raises worrying legal and privacy concerns about what happens to our DNA data once it is submitted to such sites. Genealogy companies are flourishing, offering ways for people to find out who they are related to and where their family may come from – and with that has come a whole raft of valuable data..
The data collected by such sites is arguably the most personal there could possible be, offering a picture of the unique make-up of our body. But it is being stored by companies that are private, mostly unknown and with little clarity about how the data is being used.
In the case of the Golden State Killer, police appear to have narrowed down their search after they ran old DNA through a brand new online database. But that person presumably did not explicitly consent to having their data used in such a way.
There aren't strong privacy laws to keep police from trolling ancestry site databases, said Steve Mercer, the chief attorney for the forensic division of the Maryland Office of the Public Defender.
"People who submit DNA for ancestors testing are unwittingly becoming genetic informants on their innocent family," Mr Mercer said, adding that they "have fewer privacy protections than convicted offenders whose DNA is contained in regulated databanks".
Joseph James DeAngelo, 72, was arrested on Tuesday after investigators matched crime scene DNA with genetic material stored by a distant relative on an online site. From there, they narrowed it down to the Sacramento-area grandfather using DNA obtained from material he'd discarded, Sacramento County District Attorney Anne Marie Schubert said.
Authorities declined to name the online site. However, two of the largest, Ancestry.com and 23andMe, said on Thursday that they weren't involved in the case.
DNA potentially may have played an earlier role in the case. It was just coming into use as a criminal investigative tool in 1986 when the predator variously known as the East Area Rapist and the Golden State Killer apparently ended his decade-long wave of attacks.
Mr DeAngelo, a former police officer, probably would have known about the new method, experts said.
"He knew police techniques," said John Jay College of Criminal Justice professor Louis Schlesinger. "He was smart."
No one who knew Mr DeAngelo over the decades connected him with the string of at least a dozen murders, 50 rapes and dozens of burglaries from 1976 to 1986 throughout the state.
After he was identified as the suspect, however, prosecutors rushed to charge him with eight killings.
In addition, police in the central California farming town of Visalia said on Thursday that Mr DeAngelo is a suspect in a 13th killing and about 100 burglaries in the area.
In 1975, community college teacher Claude Snelling was shot while trying to stop a masked intruder from kidnapping his 16-year-old daughter from his home.
Investigators lacked DNA evidence, so Snelling's death and the burglaries weren't included in the tally of Golden State Killer crimes, but fingerprints and shoe tracks will be reviewed for matches to Mr DeAngelo, Visalia Police chief Jason Salazar said.
Investigators searched Mr DeAngelo's home on Thursday, looking for class rings, earrings, dishes and other items that were taken from crime scenes as well as weapons.
Meanwhile, Mr DeAngelo's neighbours, relatives and former acquaintances all say they had no inkling that he could be a serial killer. He worked nearly three decades in a Sacramento-area supermarket warehouse as a truck mechanic, retiring last year. As a neighbour, he was known for taking meticulous care of his lawn in suburban Citrus Heights.
Mr DeAngelo worked as a police officer in the farming town of Exeter, not far from Visalia, from 1973 to 1976.
Mr DeAngelo was a "black sheep" who didn't joke around with other officers, said Farrel Ward, 75, who served on the force with Mr DeAngelo.
Mr Ward said it's possible that Mr DeAngelo helped with the search for Snelling's killer and the elusive burglar but he doesn't recall Mr DeAngelo directly investigating the killing.
"I've been thinking, but there's no indication whatsoever that anything was wrong," Mr Ward said.
"How could you just go out and kill somebody and go back and go to work? I don't understand that."
Later, Mr DeAngelo joined the Auburn Police Department outside of Sacramento but was fired in 1979 after he was caught shoplifting a hammer and dog repellent.
Investigators say they have linked Mr DeAngelo to 11 killings that occurred after he was fired.
James Huddle said he always hoped police would catch the killer whose attacks prompted him to buy a pistol.
But he was stunned to find out the man arrested was Mr DeAngelo, his former brother-in-law.
Mr Huddle said it was "still just going crazy in my mind".
Additional reporting by Associated Press