For decades, police say the Golden State Killer DNA was kept as evidence: a unique genetic fingerprint that could undeniably identify the man who killed 12 people and raped 45 women in California between 1976 and 1986
And for decades, those samples were basically useless for researchers, who came across the same wall that has foiled the police since the invention of forensic DNA: a genetic fingerprint is not very good unless you already know who belongs
The killer was, apparently, not one of the millions of convicts, criminals and arrested in the FBI's national DNA database. The genetic samples from all those crime scenes simply identified the Golden State Killer as a large intermittent question mark.
Until this week, when police announced they had crossed the wall and identified Joseph DeAngelo as the suspected Golden State killer using a clever technique that thrills law enforcement officials and disturbs privacy advocates:  They tracked their suspect through their family tree.
Police said they reviewed the DNA of the crime scene against one of the genealogy sites profiles of people who voluntarily offer their genetic codes in the hope of discovering their relatives and ancestors. GEDmatch, a free service, confirmed that the police used it to identify DeAngelo.
The Golden State Killer was not in this database either, but it did not matter. A distant relative of him was, says the police, and that person's DNA partially coincided with the serial killer. Instantly, the group of suspects was reduced from millions of people to a single family.
Detectives then used traditional investigative techniques to reduce family members to a suspect: Joseph James DeAngelo, a 72-year-old former police officer who lived a few miles from many of the attacks.
If DeAngelo is in fact one of the most notorious serial killers in US history. UU., His arrest on Tuesday is a milestone in the short history of DNA family searches, a technique that is still outside of forensic science, and that some people think should stay there, lest it make us all in potential informants.
Others, however, think that it could lead to a world in which no criminal would feel safe, lest one day the DNA of a distant cousin take the police to his door.
Police began scanning fingerprints in 1985, a year before the Golden State Assassin raped and beat his last known victim. It was used to convict Florida rapist Tommie Lee Andrews two years later, Time magazine reported – then a series of other criminals, until it became common for police to obtain DNA samples from suspects to use as evidence in court .
The FBI created a database of DNA profiles in the 1990s and police lined up to verify their samples of evidence against them, hoping that their suspect might be an ex-convict, or already incarcerated , or otherwise in the system. The method even allowed the police to solve old cold cases, some of them committed long before the DNA tests existed.
But the database was of little help if the owner of the DNA was not there.
One of the first cases in which the genes of a family member took the police to a suspect took place in Britain. The mutilation and murder of Lynette White on Valentine's Day in 1988 was one of the most notorious unresolved cases in the country, the BBC wrote. Three men had been wrongly imprisoned for the crime. A massive police hunt had failed to find the real killer.
But in the early 2000s, the BBC wrote that police found a new DNA sample at the crime scene, "under layers of paint on a skirting board." it did not match any profile in the national database of Britain, but it partially coincided with a 14-year-old boy whose DNA was archived after an altercation with the police.
The boy was born after the murder, obviously, but unconsciously he took the police to his uncle, who quickly confessed the murder.
Police in Los Angeles had a similar stroke of luck in 2010, when the DNA of Grim Sleeper, a serial killer that had not been detected for decades, was partially matched by a man in the prison system. That man turned out to be the killer's son, reported the Los Angeles Times. The Grim Sleeper was identified as Lonnie David Franklin Jr. and sentenced to death.
These cases, however, were still based on DNA obtained by the police or by court orders, if not from the suspect himself, then from a family member.  It's only in recent years, when millions of people have sent DNA samples to sites of descent, that the police have used family DNA searches to read science fiction, whether you find them hopeful or horrifying .
Take the Killer Channel case: a double murder in Phoenix that had not been resolved since the early 1990s. The suspect's DNA was on file, but it does not match anyone in the FBI database.
Then, in late 2014, the Arizona Republic wrote that the police met with a genealogist at a conference and told him about the case. The researchers eventually sent the genealogist, who did not even live in the state, a profile of the DNA sequence of the Killer Channel.
Two months later, the newspaper wrote, the genealogist sent an email to the probable surname of the suspect: Miller.
This was not a psychic intuition, reported the Republic, but the result of searches of the genealogist ran on Family Tree DNA and Ancestry.com, two of the most popular databases.
That last name led the police within a few weeks to suspect Bryan Patrick Miller of the murders. They secretly collected their DNA, possibly from a bottle or discarded trash, the Republic wrote, and they arrested him, claiming he had the same genetic fingerprint as the Killer Channel.
On the more dystopian side of the spectrum, Wired reported on a filmmaker named Michael Usry who was charged with murder in 1996 in Idaho Falls nearly 20 years after the fact, coincidentally the same month that the Phoenix police got their chance in the Killer Channel research.
Usry, who was a teenager at the time of the murder, was picked up by police at his door in New Orleans in December 2014, Wired wrote. He was interrogated by an FBI agent and spent a month under suspicion, all because the genetic code of the murderer was similar to that of his father, whose DNA sample had been obtained by Ancestry.com.
But unlike Bryan Patrick Miller and Joseph DeAngelo, Usry DNA testing discarded him as a suspect. His father was one of the many false positives that plague familiar DNA tests, Wired wrote.
"He looked like a good candidate," an Idaho Police Sgt. Fall to the New Orleans Ombudsman said after Usry was acquitted. "But we've had to go before."
Family DNA searches, in fact, had an 83 percent failure rate in a British study in 2014, Wired wrote. This is part of the reason why many warn against the practice, even when law enforcement agencies dominate their uses.
"The technique is raising fierce objections from privacy advocates, who argue that it turns family members into genetic informants without their knowledge or consent, "Ellen Nakashima wrote in The Washington Post in 2008, long before the popularity of genealogical sites exploded.
Wired reported that Maryland and the District of Columbia banned family DNA searches, while the method is regulated in several other states, including California, where police used it to locate the suspected Golden State killer.
"You allow that low quality, potential evidence to start looking at these unregulated databases," Stephen Mercer, a former public defender who helped approve the family search ban in Maryland, told The Post. "You are casting a wide network of suspicions about many people."
Aware that their millions of clients do not necessarily want to inform their relatives, some genealogy companies are actively resisting to give data to the police, STAT wrote this week.
23andMe, one of the oldest and most popular DNA search companies, has rejected all requests for application of the law, the publication wrote. Ancestry too, at least since 2014, when the police used their database to falsely accuse Usry of the Idaho Falls murder in 1996.
However, California researchers did not use any of those sites to find the family of the Golden State killer. . Rather, they allegedly ran their previous evidence through GEDmatch, a relatively small and free service that allows users to upload and analyze their DNA sequence.
"We understand that the GEDmatch database was used to help identify the Golden State Killer," the company said in a statement. "Although we were not approached by law enforcement or any other person on this case or on DNA, it has always been GEDmatch's policy to inform users that the database could be used for other uses."
It is precisely these other uses that now, after the sensational break of a 40-year serial killer case, excite and alarm so many people.
"I think it's revolutionary," Richard Shelby, a former detective with the Sacramento County Sheriff's Department who persecuted the Golden State Killer in the 1970s, told The Post after this week's arrest.
"If the criminals know they can be tracked in this way, they will have to try not to leave their DNA on the scene and that is almost impossible," he said. . "It's one of the best tools to fight crime in a long, long time."
Justin Jouvenal, Drew Harwell and Tom Jackman contributed to this report.
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