While ubiquitous now in some of our favorite true crime shows, the technique of using DNA samples to identify potential criminals started making its way into the forensic world by chance — and still is not as popular or helpful as one might think.
Who Invented DNA Profiling?
The method for DNA profiling as we know it today is largely attributed to Sir Alec Jeffreys, a British geneticist. Jeffreys' groundbreaking work led to real-world applications, from immigration disputes to solving heinous crimes.
When he first talked about how helpful this could be in real life — for paternity tests or rape cases — many of his colleagues "fell over laughing," he says in the interview.
When Was the DNA Fingerprint First Discovered?
On a Monday morning in 1984 — Sept. 10 at 9:05 a.m., to be exact — Jeffreys was in his lab at the University of Leicester in the U.K. when he accidentally discovered that our DNA strands are unique enough to be accurately linked to their owners.
He and his team were running an experiment to track down inherited diseases, and were extracting DNA from cells and using photographic film to develop them like pictures — when they saw a pattern they couldn't unsee.
"We got this fuzzy, splodgy mess, but the DNA fingerprint was absolutely obvious. We got a pattern like a fuzzy bar code," Jeffreys tells Plos Genetics in an interview about the experiment. "These patterns were individual-specific and seemed to be inherited within the family. That was a real eureka moment because we were suddenly onto something completely new, which was DNA-based identification."
Soon after, in 1985, Jeffreys helped provide scientific evidence for an immigration dispute by matching a boy to his biological parents through DNA to allow him British citizenship. Until 1987, his lab was the only one in the country providing this sort of testing for civil cases like these.
Read More: Taking a Closer Look at Forensic Science Behind U.S. Criminal Justice
When Was DNA Evidence First Used?
DNA evidence was first used in the criminal case of Lynda Mann and Dawn Ashworth in 1986. The police approached Jeffreys's team, asking for help on a double rape and murder case of two teenagers from Narborough, just 5 miles southeast of his university.
Though the crimes were two and a half years apart, 15-year-olds Lynda Mann and Dawn Ashworth had both been raped and murdered, in very similar ways, on their way back from school. The police were looking for a serial killer and had their eyes set on 17-year-old Richard Buckland.
What Is Significant About the Lynda Mann and Dawn Ashworth Cases?
The Lynda Mann and Dawn Ashworth cases became a milestone in the history of forensic science, as the cases demonstrated the potential of DNA evidence in identifying and capturing criminals. They also ultimately led to the development and widespread use of DNA profiling in criminal investigations.
Wanting to confirm that Buckland was responsible for both the deaths, the police provided Jeffreys with semen from Buckland and the two crime scenes.
"I have to say that was a chilling moment," says Jeffreys in his interview with PLOS. "An ordinary academic, and suddenly you've got murder samples in front of you."
What Did Richard Buckland's DNA Evidence Reveal?
Richard Buckland's DNA evidence revealed that he was not the perpetrator in the double rape and murder case. Jeffreys' team ran the DNA test on the semen samples three times because although the DNA from both rape kits was the same, it definitely didn't match with Buckland's — who was therefore released thanks to this discovery.
"The results were totally astonishing, totally overturned what the police had got fixed in their minds about the guilt of this prime suspect," says Jeffreys.
Using this tech and replicating this experiment, a team of British Home Office forensic scientists recruited as many men as possible from the town and neighborhood of the two murder cases and worked to find a match with the DNA found at the crime scene. Given the town's size and the case's gruesomeness, almost everybody voluntarily joined in.
The irony in this case is that it wasn't the actual DNA that caught the killer — but the possibility of DNA catching the killer.
How Was Colin Pitchfork Found?
Investigators arrested Colin Pitchfork in September 1987 for the rape and murder of Lynda Mann and Dawn Ashworth. More than a year after the last murder, a man in a pub confessed to his friends that, as a favor, he had actually pretended to be their colleague — 27-year-old father of two Colin Pitchfork — for the DNA testing. When the police got wind of this, they called Pitchfork in for questioning; he confessed to the crime almost immediately. DNA testing then confirmed him as the perpetrator.
After this case, investigators and scientists rapidly implemented the novel technique across the country, and the whole world soon followed. "It was this case that triggered the application of molecular genetics to criminal investigations worldwide, with DNA profiling remaining the standard technology well into the 1990s," writes Jeffreys.
Read More: Top 5 Pieces of Forensic Evidence Used to Solve a Crime
How Was DNA Initially Used In Forensics?
For a while after the first use of DNA evidence, investigators only used it as a forensic tool "in very big cases, and not that often, because it was just so cumbersome," says Carole McCartney, a professor of law and criminal justice at the University of Leicester — where Jeffreys first discovered DNA could be used in forensics.
When Did DNA Evidence Become Common?
It was only when entire countries started compiling their own national DNA databases that the technique could really become popular, says McCartney. The U.K. established its National DNA Database in 1995; by 2023, it has over 5.9 million registered people.
DNA used in forensics "took off to be massive" at this point, according to McCartney, until the European Human Rights Court started cracking down on not wanting innocent people's data profiled and stored in police databases, seeing it as an infringement on the "right to a private life."
Read More: How Indirect DNA Transfer Is Challenging Forensics and Overturning Wrongful Convictions
How Many Criminal DNA Profiles Does the U.S. Have?
As of the end of 2022, in the U.S., the National DNA Index System has DNA information for more than 15.7 million offenders and more than 4.8 million arrestees. Since 2002, an international DNA database has also existed — INTERPOL's DNA database — which currently has more than 280,000 people profiled from almost 90 countries.
Are There Any DNA Ethical Issues?
The proportion of non-whites in forensic DNA databases of both the U.K. and the U.S. is significantly higher than the proportion of non-whites in the countries' general populations. In many cases, collection policies extend bias (whether conscious or subconscious), rather than guarding against it.
In the U.S., for instance, DNA is collected from Black persons - including those arrested and later found innocent - at a rate two to three times that of whites. (On the other hand, genetic profiles used for health and population genomic research are heavily skewed towards those of European background, while non-whites are underrepresented.)
There is also the possibility of basic human error and human bias in using these samples. In an often-cited 2011 paper on the topic, researchers found that as 17 DNA experts were asked for their take on DNA data from an adjudicated criminal case, "they produced inconsistent interpretations," and, specifically, the experts who didn't have any context disagreed with the lab's conclusions.
Read More: Why We Are Fascinated With Serial Killers
Is DNA or Fingerprinting More Common?
Fingerprinting is more commonly used than DNA evidence. Today the original DNA technology that Jefferys' team first used to convict Pitchfork isn't really used much anymore — not only has the technique been advanced, simplified, and sped up, but it also never really was the Holy Grail of solving crimes, according to McCartney.
DNA Isn't as Successful as Fingerprinting
"We don't actually use DNA a whole lot. It's not particularly that successful," says McCartney. "For years, I've been banging the drum that if you look at it, through bare figures, our [U.K.] DNA database solves 0.3 percent of crimes a year. It hasn't lived up to everybody's expectations."
Fingerprinting Is Less Costly Than DNA
DNA testing has never been more successful than fingerprinting, which is cheaper and quicker, says McCartney, and it is mainly used in interpersonal violence cases with a lot of other evidence at hand, too. Perpetrators leave behind DNA in less than 10 percent of murders, according to The Innocence Project.
Lack of DNA Technology
In addition, the fact that the tech exists isn't enough for it to be correctly implemented at all times. According to McCartney, police forces often do not have the funding or forensic expertise available to carry out DNA testing or store DNA evidence correctly and at appropriate temperatures.
"The police don't take the evidence and then don't store it properly," says McCartney. "It takes diligence and money and intelligence and stuff to use the technology, which a lot of the time we don't actually have."
"We could catch an awful lot more people by just doing the basics properly," says McCartney.
Read More: The First Criminal Conviction Based on Fingerprint Evidence
How Is DNA Evidence Used Today?
While DNA evidence isn't typically the number one resource used for solving crimes, it has been instrumental in exonerating individuals who were wrongly convicted. It can prove a person's innocence and lead to the release of individuals who have been imprisoned for crimes they did not commit.
"The big thing, of course, is that it's been absolutely brilliant in exonerating people and showing up how crap a criminal justice system is," says McCartney. "Because we prosecute the wrong people, and DNA can almost definitively show people's innocence."
As it did for Buckland, for instance, since 1989, in the U.S., 575 wrongly convicted people have been exonerated based on DNA samples, according to the National Registry of Exonerations — 35 of whom were on death row.
