Testing DNA samples in criminal investigations is as much about scientific ingenuity as it is about dogged police work and the pursuit of justice for crime victims. The technology came to prominence in an era when unreliable eyewitnesses and forced confessions sometimes carried more weight in court than tangible scientific evidence.
As the doors to the molecular world opened to aid in crime solving, so did new possibilities for justice—sometimes decades after crimes were committed.
Here’s how the history of DNA evidence in criminal cases unfolded.
1986: Law Enforcement Tests DNA For First Time
Seeking evidence in Britain in 1986 to prove allegations that teenager Richard Buckland raped and murdered Lynda Mann and Dawn Ashworth, both 15, homicide investigators enlisted geneticist Alec Jeffreys to conduct the first forensic testing of a suspect’s DNA.
Jeffreys had figured out how to extract DNA cells and attach them to photographic film that would show a sequence of markers that showed up on the film looking like a unique bar code. The sequence could be used to identify the person from whom the cells came.
Jeffreys carried out tests on Buckland’s blood and on semen taken as evidence from the girls’ bodies to compare the DNA of each sample. Buckland was cleared because the DNA for the semen did not match his DNA from the blood. Authorities then collected blood samples from more than 5,000 men who volunteered to provide DNA, but that testing failed to make a match.
In 1987, investigators learned that one of the test subjects had admitted to impersonating another man, Colin Pitchfork, a baker who had been questioned about his whereabouts the night of Mann’s murder. Pitchfork, it turned out, had recruited the man to pretend to be him and take the DNA test.
Police arrested Pitchfork, who confessed to sexually assaulting and killing the girls. DNA testing confirmed the semen collected at the crime scenes matched Pitchfork’s blood.
1988: DNA Evidence Helps Convict Serial Rapist
Identifying a suspect with DNA samples made its way to the U.S. in 1988 after a Florida prosecutor read about the Mann and Ashworth investigation.
Florida officials then delivered DNA samples collected in six rape cases that law enforcement believed had been committed by Tommie Lee Andrews, who was detained following his arrest in one of the sexual assaults. Police claimed Andrews may have been responsible for more than 20 rapes in the greater Orlando area.
Andrews’ DNA matched evidence found in two cases, and in 198,8 he became the first person to be convicted in the U.S. with DNA evidence. He was convicted of raping two women and was sentenced to more than 100 years in prison, but got his sentence reduced to 25 years following an appeal and credit for good behavior behind bars. Andrews was released in 2021.
The successful use of DNA testing in Andrews’ conviction kickstarted its practice across law enforcement laboratories nationwide. Civil libertarians also turned to DNA testing to correct miscarriages of justice, such as the 1979 conviction of Illinois inmate Gary Dots,on who was serving 25 to 50 years' imprisonment for rape and 25 to 50 years for aggravated kidnapping.
In 1988, Dotson was among the first people in the U.S. to be exonerated by DNA evidence. Authorities had retested a semen stain found on a victim and it did not match the DNA of Dotson, who had been wrongfully locked up for nearly a decade.
1990s: DNA Testing Takes Off Amid Skepticism
As the number of cases solved by DNA grew, so did the calls to standardize and automate the process of DNA testing in forensic crime analyses.
In 1990, the FBI established CODIS, the Combined DNA Index System, a database for the collection of DNA profiles from convicted offenders and unsolved crime scenes.
CODIS significantly boosted the collection of DNA samples available for comparison, giving police agencies the ability to match unknown profiles from crime scenes to previous offenders and to other unsolved cases, allowing authorities to identify and prosecute serial rapists and killers who might have otherwise escaped detection.
DNA Evidence in the ‘Trial of the Century’
DNA testing took center stage during the “Trial of the Century” when retired football star O.J. Simpson was accused in 1995 in the double murders of his ex-wife Nicole Brown Simpson and her friend Ronald Goldman. Both were stabbed to death outside Nicole’s home in Los Angeles.
During the trial, prosecutors presented evidence of the victims’ blood at the crime scene matching blood found on the door of Simpson’s car, on his socks and on black leather gloves he owned.
One glove was found outside Nicole’s house and the other glove was seized from Simpson’s residence. But Simpson’s legal dream team effectively assailed how police mishandled the DNA evidence, including storing crucial blood samples in a police van without air conditioning or placing it in plastic bags that subjected the evidence to contamination.
Prosecutors also made a huge mistake in having Simpson try on the gloves in front of the jury. He struggled in his attempt to make the gloves fit his fingers.
Simpson, who was found not guilty, died of cancer in 2024. His trial had lasted eight months and prompted a national conversation about DNA, forensics and the limits of scientific certainty in justice.
DNA Testing Leaps into a New Century
Genetic labs worked hard to improve testing methods. Early DNA analysis required copious amounts of biological material, such as a prominent bloodstain to produce acceptable and accurate results. But by 1997, a mere trace—a few skin cells or a saliva smear from a cotton swab—was enough to generate a robust DNA profile.
Forensic DNA testing became routine by the early 2000s, rapidly providing answers in new and decades-old cases. In 2001, DNA identified victims from the 9/11 terror attacks. In 2018, forensic genealogy, which relies on ancestry databases, helped authorities identify and arrest Joseph James DeAngelo as the Golden State Killer. For decades, DeAngelo was among America’s most notorious unidentified serial killers and serial rapists.
Investigators compared DNA collected from one of the Golden State Killer’s crime scenes to online genetic profiles. They matched the DNA to a distant relative of DeAngelo. In 2020, the former police officer pleaded guilty to 13 murders and 13 rapes and began serving 11 consecutive life sentences.
All 50 U.S. states have laws mandating DNA collection of samples from convicted felons. Thousands of DNA labs exist worldwide. Modern analysis allows DNA profiles of different people to be extracted from samples that have DNA of various people mixed together.
Law enforcement agencies are also utilizing rapid DNA machines, devices that generate a human DNA profile within about 90 minutes. The machines eliminate the need for traditional DNA analysis that can take weeks. Deputies in the Naples area of Southwest Florida used a rapid DNA machine to identify a suspect in a stabbing homicide after matching the victim’s blood to a sweatshirt worn by the killer.
The DNA testing that began with a criminal investigation in England has become a global force that reshapes justice with tiny drops of blood, saliva or other genetic material.
