It’s been almost four years to the day since Joseph James DeAngelo, the infamous American serial killer known as the Golden State Killer, pleaded guilty to crimes including rape and murder. When he did so, it marked the beginning of a new era in crime-solving – the age of Forensic Investigative Genetic Genealogy (FIGG).
DNA testing has been used to match crimes to criminals for decades, but when police lack a suspect to test DNA samples against, cases can hit a brick wall. That’s where FIGG comes in.
“Using DNA databases, you can find people who are genetic relatives of DNA found at the crime scene,” Dr Turi King told BBC Science Focus at the Cheltenham Science Festival.
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“You can look and see that someone on the database shares a certain amount of DNA with the perpetrator; maybe they’re a second or third cousin or something. And then you might ask: ‘Okay, who are their grandparents?’”
King explained that police and experts then start building a family tree outwards from the DNA match until they find someone who could have feasibly committed the crime. If someone crops up on the family tree who was nearby when the crime occurred, or who matches other evidence like witness statements, then law enforcement can look at them as a suspect.
For former cop DeAngelo, who committed his violent crimes across California between 1974 and 1986, his downfall came about when genealogists uploaded analysis of crime scene DNA to consumer ancestry website GEDmatch.
Suddenly, a service used by the public to find long-lost relatives was being used by law enforcement to catch a serial killer. They tracked down DeAngelo, obtained some of his DNA, and arrested him in April 2018. He was sentenced to life imprisonment in August 2020.
Since DeAngelo’s arrest, over 500 cases have been solved using FIGG. As more and more people upload their DNA to online databases, the chances of using it to catch a killer are increasing all the time.
Obviously, there are some pretty big ethical considerations raised by the prospect of using public DNA data to catch and prosecute criminals.
For King, it’s all about informed consent – that people know their DNA profiles could be used in this way and that precautions are taken to keep them safe.
“If I'm on a database and I help lead the police to somebody who's a killer, who might strike again, then that's really a good thing to do,” she said.
“But I can see where the issues are. There have been cases, for example, where a genetic match that led police to an individual was named in a police document, which means the perpetrator knows who they are.”
“And while this person is completely innocent in terms of why they've uploaded their DNA, you don't know what the perpetrator is going to do with that information. So you can understand how people might be a bit nervous.”
Where could all of this lead?
Ethical considerations aside (and hopefully resolved), King is confident that FIGG has an important role to play in solving serious crimes in the future. For many cold cases across the US and Canada, she said, it already has.
But should we stop there with DNA techniques? Or could our genetic code help crime fighters in other ways?
One interesting, albeit hypothetical, example King raises is using surnames.
She explained that genetic markers on the Y chromosome – the one which, if present, determines that a foetus develops into a male – are passed down through male lineages. Thus, you can follow male lines back through family histories, tracing the same Y chromosome types as you go.
Though not as iron-clad as genetic markers, surnames follow a similar pattern to Y chromosome types in that they’re usually passed down the male line. Could there be a link between the two?
As it turns out, yes. Even though some surnames like Smith or Jones are very common, King explains that the average number of 'carriers' per surname in the UK is only around 70. When you look at the data, it’s therefore possible to match identical Y Chromosome types to people’s surnames.
“So you could go to a crime scene and pick up a Y chromosome type, put it into some database and predict possible surnames,” King explains. “If you get the surname of someone already on your suspect list, and it’s quite an unusual surname, then you could interview them first and do standard DNA testing.
“It would be a way of narrowing down your list. It’s not evidential, but investigative,” she said.
It's been estimated that this technique could be used to solve about 70 rapes or murders per year. So, should we expect to be getting pulled into interview rooms because of our last names anytime soon?
Not likely, King said. “It’s a really interesting hypothetical, and it’s feasible, but it would be difficult to put into effect because you’d need such a massive database.”
About our expert
Turi King is a scientist, presenter, speaker and author who is passionate about communicating science to the public. She’s worked in the field of genetic genealogy since 2000 and is perhaps best known for her work cracking one of the biggest forensic DNA cases in history – confirming the identity of King Richard III in 2013.
Her award-winning PhD examined the relationship between the Y chromosome and British surnames combining forensic DNA techniques with history and genealogy, the first large-scale study of its kind.
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