Police first used DNA to solve a crime in 1986, when British investigators in Leicestershire, England applied a new genetic fingerprinting technique to identify a double murderer. American prosecutors followed quickly: in November 1987, a Florida jury returned the first U.S. criminal conviction based on DNA evidence. So the short answer to when police started using DNA in criminal cases is the mid-to-late 1980s, with the technique moving from a single English investigation to courtrooms on both sides of the Atlantic in roughly two years.
The Science That Made It Possible
Forensic DNA rests on a simple biological fact: except for identical twins, no two people share the same genetic code. Researchers identified DNA’s double-helix structure in 1953, but three more decades passed before anyone found a way to use genetic differences to tell individuals apart.
That breakthrough came in 1984, when geneticist Alec Jeffreys at the University of Leicester discovered that certain regions of DNA vary dramatically from person to person. By analyzing those variable regions, Jeffreys could produce a visual pattern unique to an individual, which he called a “genetic fingerprint.”1National Library of Medicine. Alec Jeffreys and the Pitchfork Murder Case His method, known as restriction fragment length polymorphism (RFLP) analysis, cut DNA strands at specific points and sorted the resulting fragments by size. Different people produced fragments of different lengths, creating a distinct profile.2National Institute of Justice. Crime Scene and DNA Basics for Forensic Analysts – DNA Typing by RFLP Analysis
Within two years, police would ask Jeffreys to put the technique to work on a real case.
1986: The First Criminal Investigation to Use DNA
Police in Narborough, Leicestershire were investigating the rapes and murders of two teenage girls. They had a suspect in custody and asked Jeffreys to compare the man’s DNA with evidence from the crime scenes. The profiles did not match. It was the first time DNA evidence had been used to clear someone in a criminal investigation.1National Library of Medicine. Alec Jeffreys and the Pitchfork Murder Case
With their original suspect ruled out, investigators turned to a mass screening, collecting blood samples from thousands of local men. A baker named Colin Pitchfork tried to beat the dragnet by persuading a friend to submit a sample in his place. The scheme unraveled when the friend was overheard talking about it. Pitchfork’s DNA matched the crime scene evidence, and he was convicted in 1988.
The Pitchfork case did two things at once. It identified a killer who might otherwise have gone free, and it exonerated an innocent man already in custody. No earlier forensic technique had done both in a single investigation.
1987: DNA Reaches American Courts
DNA evidence crossed the Atlantic almost immediately. In November 1987, a Florida court convicted Tommy Lee Andrews of rape partly on the strength of DNA analysis. It was the first DNA-backed criminal conviction in the United States. By the late 1980s, prosecutors across the country were presenting DNA evidence in court, and defense attorneys were starting to challenge it, which set up the legal battles that would decide whether the technique belonged in a courtroom at all.
How Courts Decided DNA Was Reliable Enough to Use
Admitting a new scientific technique as evidence requires more than confidence from the people who developed it. For most of the 20th century, federal courts followed a rule from the 1923 case Frye v. United States, which required that the method behind the evidence have “general acceptance” in the relevant scientific community.3New York State Federal Judicial Center. Frye v. United States DNA evidence generally cleared that bar by the early 1990s, as the scientific community reached broad agreement on its reliability.
In 1993, the Supreme Court replaced Frye in federal courts with a more flexible framework in Daubert v. Merrell Dow Pharmaceuticals. Under Daubert, the trial judge acts as a gatekeeper and evaluates whether the methodology behind expert testimony is scientifically valid. The judge weighs whether the technique has been tested, whether it has known error rates, whether it has undergone peer review, and whether it is generally accepted in its field.4National Institute of Justice. Daubert and Kumho Decisions Most states have since adopted the Daubert standard or something close to it, and a handful still follow Frye. Under either framework, DNA is now routinely admitted in criminal trials.
From Single Cases to a National Database
Individual case results in the late 1980s were striking, but each investigation still required police to have a suspect to compare against. Centralized databases changed that. The FBI launched its Combined DNA Index System (CODIS) as a pilot in 1990, initially connecting just 14 state and local laboratories.5Federal Bureau of Investigation. Combined DNA Index System (CODIS) Congress formalized the system four years later with the DNA Identification Act of 1994, which authorized a national DNA index.6Federal Bureau of Investigation. CODIS and NDIS Fact Sheet
CODIS compares DNA profiles from crime scenes against profiles from convicted offenders and, in many states, people arrested for qualifying offenses. When a crime scene profile matches someone already in the database, investigators get a lead they would not have found through traditional detective work. The system also links serial crimes committed in different jurisdictions by matching forensic profiles to one another.5Federal Bureau of Investigation. Combined DNA Index System (CODIS) The United Kingdom built a parallel system, establishing its National DNA Database in 1995.7ScienceDirect. The Effectiveness of the UK National DNA Database
How the Toolkit Grew After the First Cases
The RFLP method Jeffreys used in 1986 needed relatively large, well-preserved samples and could take weeks to produce results. The development of polymerase chain reaction (PCR) technology changed that. PCR copies tiny fragments of DNA millions of times, which makes it possible to analyze samples as small as a pinhead or evidence that has partially degraded.8National Institute of Justice. Polymerase Chain Reaction (PCR)
By the mid-1990s, forensic labs had largely moved to a PCR-based technique called short tandem repeat (STR) analysis, which remains the standard today. STR typing examines specific locations on the genome where short DNA sequences repeat a variable number of times. Because the number of repeats differs from person to person, checking enough locations produces a profile that is statistically unique.9National Center for Biotechnology Information. Forensic DNA Profiling: Autosomal Short Tandem Repeat as a Gold Standard in Criminal Investigation
The Rapid DNA Act of 2017 authorized police booking stations to use FBI-approved instruments that can generate a profile from a cheek swab in roughly two hours without a trained lab technician, and to upload the resulting profiles directly to CODIS.10Congress.gov. H.R.510 – Rapid DNA Act of 201711Federal Bureau of Investigation. Rapid DNA
Investigative Genetic Genealogy
In April 2018, California investigators announced the arrest of Joseph James DeAngelo, a former police officer suspected of being the Golden State Killer, a serial offender linked to at least 13 murders and 50 sexual assaults in the 1970s and 1980s. His DNA was not in CODIS. Investigators uploaded crime scene DNA to GEDmatch, a public genealogy database, identified distant relatives of the unknown suspect, and traced family trees outward until they narrowed the field to DeAngelo. They confirmed his identity with DNA collected from a discarded item.
The Department of Justice issued an interim policy in 2019 for federal agencies and federally funded investigations that use genetic genealogy. The policy limits the technique to serious violent crimes and unidentified human remains, and it requires that traditional DNA database searches come up empty before investigators turn to public genealogy sites.12United States Department of Justice. Interim Policy: Forensic Genetic Genealogical DNA Analysis and Searching State and local agencies operating outside federal funding are not bound by those restrictions.
DNA Exonerations
DNA evidence has not only put people behind bars. In 1993, Kirk Bloodsworth became the first person in the United States exonerated from death row through post-conviction DNA testing. He had been convicted of murder in 1985 based largely on eyewitness testimony, and DNA analysis of the crime scene evidence proved he was not the perpetrator. Hundreds of wrongful convictions have since been overturned with the help of DNA analysis, often revealing that eyewitness misidentification, false confessions, or flawed forensic techniques had driven the original verdict.13Office of Justice Programs. Post-Conviction DNA Testing and Wrongful Conviction Many states now guarantee convicted individuals the right to request DNA testing of preserved evidence.
Four decades on from the Pitchfork investigation, DNA has gone from a single geneticist’s laboratory technique to a routine part of police work, courtroom evidence, and post-conviction review. The starting point, though, is fixed: 1986 in England, and 1987 in the United States.