At 9:05 on the morning of Monday, September 10, 1984, in a genetics laboratory at the University of Leicester, Alec Jeffreys realized that human DNA could produce patterns unique to each person, a technique that became known as DNA fingerprinting. Within two years the technique had been carried out of the laboratory and into a double murder inquiry a few miles south of the city, and its first act in a criminal case was to clear a suspect who had confessed.
What followed over the next four decades was not one breakthrough but a series of them, each arriving through a particular case. A village blood screen in Leicestershire. A courtroom fight in Virginia over whether juries could be trusted with the new science. A Canadian trial in which the argument shifted from whether the bands matched to how rare the match really was. Saliva kept in a Washington evidence room for fourteen years. A California offender data bank that named a killer and freed an innocent man in the same review. A Scottish acquittal undone by a new law and a new light source. A list of a thousand possible relatives in Kent. And finally, in California, the turn from criminal databases to the family trees of ordinary people.
Lynda Mann was 15 when she was killed in Narborough, Leicestershire, in November 1983. Dawn Ashworth, also 15, was killed in the neighboring village of Enderby in July 1986. Police believed one man was responsible for both deaths, and in 1986 they had a suspect: R.B., a local teenager who confessed to Dawn’s murder but denied any part in Lynda’s.
Detectives took their samples to Jeffreys. His result showed that the same man had killed both girls and that it was not R.B. He was released. In a 2017 statement to a United States House Judiciary subcommittee, its chairman, Bob Goodlatte, described him as the first person exonerated through DNA testing, and quoted Jeffreys as saying he had "no doubt whatsoever" that R.B. would have been convicted without it.
With its suspect gone, Leicestershire Police asked the men of the surrounding villages to give blood and saliva so that they could be eliminated, and about 5,000 of them came forward. None matched. The man police wanted had arranged it that way. According to the Parole Board for England and Wales, Colin Pitchfork, a married baker who lived in the area, paid a work colleague to attend the testing in his place, fixing the colleague’s photograph into his own passport; the colleague practiced Pitchfork’s signature and gave a sample in his name. When the deception came out, Pitchfork’s own DNA was tested and matched the profile from both killings.
On January 22, 1988, after guilty pleas at Leicester Crown Court, he was sentenced to life imprisonment for the two murders, with concurrent terms for the other offenses, among them perverting the course of justice through the substitute sample. ITV News, marking the case in 2023, called him the first person in the world convicted with the help of DNA fingerprinting. Jeffreys told the broadcaster that the technique "does not solve crimes. It establishes whether sample X comes from person Y."
The minimum term was fixed at 30 years by the Home Secretary in 1994 and again by the High Court in 2008, then reduced on appeal in May 2009 to 28 years. Pitchfork was released on license on September 1, 2021, and recalled on November 19, 2021. In a decision dated October 27, 2025, the Parole Board refused to direct his release or to recommend his return to open conditions.
In the autumn of 1987 three women and a teenage girl were killed in Virginia. Debbie Dudley Davis, 35, died in Richmond; her death came to light on September 19, 1987. Dr. Susan Hellams, 32, a neurosurgery resident at the Medical College of Virginia, died in Richmond in the early hours of October 3. Diane Cho, 15, a high school freshman whose parents had recently come to the area from Korea, died in Chesterfield County; her death came to light on November 22. Susan Tucker, 44, a writer, died in Arlington around Thanksgiving; her death came to light on December 1. Richmond’s press called the unknown killer the "Southside Strangler."
Richmond police had already sent samples to Lifecodes, a private laboratory in New York, for a test that had not yet been used to solve a homicide in the United States, Arlington Magazine reported. In Arlington, Detective Joe Horgas saw a likeness between the Tucker case and the 1984 killing of Carolyn Hamm, a 32-year-old lawyer, for which a local man, D.V., had entered an Alford plea and was serving 35 years. Horgas’s own memory of a neighborhood burglar called Timmy, from a decade before, gave him a name: Timothy Wilson Spencer, who had been released to a Richmond halfway house weeks before the first killing. He was arrested on January 20, 1988, and on March 16 Lifecodes reported that his DNA matched the evidence in the Tucker, Davis and Hellams cases.
His trial for Susan Tucker’s murder began in the Arlington Circuit Court on July 11, 1988. Judge Benjamin Kendrick held a special hearing on the DNA evidence and admitted it, while remarking that many people called it "hocus-pocus." Three scientists testified for the prosecution, and the defense could find no expert to dispute the method. On July 16 the jury convicted Spencer of capital murder and fixed his sentence at death. Arlington Magazine, ARLnow and WTVR in Richmond have each described it as the first capital murder conviction in the United States built on DNA. Richmond juries sentenced him to death twice more. In Diane Cho’s case, where the sample held too little DNA for the standard test, prosecutors turned to a newer method, PCR amplification, and a fourth jury convicted him.
The Supreme Court of Virginia upheld all four judgments. In September 1989 it held that DNA printing was reliable and had been properly carried out, and declined to adopt the Frye test that many courts then applied to new science; in June 1990 it held the PCR evidence admissible. Spencer, who maintained his innocence, was executed at Greensville Correctional Center on April 27, 1994.
The same inquiry reopened the Hamm case. The evidence there was too degraded for the testing of the time, so the route to D.V.'s freedom ran through the governor’s office, not the courts. Arlington police and prosecutors, working with the FBI’s National Center for the Analysis of Violent Crime, concluded that another person had killed Carolyn Hamm, and Governor Gerald Baliles granted D.V. an absolute pardon on January 4, 1989. Spencer was never charged with her death; it is attributed to him by the investigators, not by any verdict. In 1989 the state laboratory became the first state laboratory to offer DNA testing to law enforcement, according to the Virginia Department of Forensic Science, and Virginia created a DNA data bank for convicted sex offenders, widened in 1990 to all convicted felons.
Allan Legere was serving a life sentence for the 1986 murder of John Glendenning, a 66-year-old storekeeper at Black River Bridge, when he escaped from custody in Moncton on May 3, 1989. Over the next seven months four people were killed in the Miramichi region: Annie Flam, a 75-year-old storekeeper in Chatham, in May; the sisters Donna Daughney, 45, and Linda Daughney, 41, in Newcastle in October; and Father James Smith, a 69-year-old Roman Catholic priest, in Chatham Head in November. Families left outdoor lights burning through the night. Residents still call them "Legere lights," the CBC reporter André Veniot later wrote.
The science arrived in the middle of the manhunt. In early fall 1989 the RCMP’s Central Forensic Laboratory in Ottawa began DNA casework, and, according to the Crown prosecutor Jack Walsh, its first comparisons linked material from the Flam and Daughney cases to DNA in hair that police had taken from Legere during the Glendenning investigation three years earlier. On November 16, 1989, the RCMP publicly confirmed that DNA linked him to the killings. He was recaptured on November 24, ending a manhunt of about 201 days.
Those 1986 hair samples were themselves a legal problem. In 1988 the New Brunswick Court of Appeal had ruled that police infringed Legere’s Charter rights in taking them, the first without his consent and the second under a warrant that could not authorize it, but declined to exclude the evidence. Canadian law had no settled test for new scientific evidence, and at Burton, near Fredericton, Justice David M. Dickson spent about six weeks from April 22, 1991, hearing argument without a jury on whether DNA could go before one at all. The Crown called the head of the RCMP DNA section, John Bowen, an independent scientist who checked his work, and two population geneticists, George Carmody of Carleton University and Kenneth Kidd of Yale. The defense expert, William Shields of the State University of New York, did not dispute the laboratory work or the matches. He disputed the odds, arguing that population structure in the region made them look rarer than they were. Following a British Columbia ruling of July 1991, Dickson admitted the evidence and left the statistics to the jury.
At trial the RCMP’s figures put one five-site match at less than one in 310 million. Shields proposed a correction that would cut it to about one in 11 million; by the end, Walsh wrote, the only dispute was over how rare the matches were. On November 3, 1991, the jury convicted Legere of four counts of first-degree murder. He was sentenced to life and declared a dangerous offender. On December 16, 1994, the Court of Appeal held that DNA typing should be judged like other scientific evidence, by its relevance and reliability, and upheld its use. Walsh later called the case one of the first criminal cases in Canada to use DNA evidence and the first serial murder case to do so. Legere was refused parole in 2021 and again in 2025, and he died in custody at Edmonton Institution on March 9, 2026, aged 78.
The Green River investigation in King County, Washington, began in 1982 and was still without a charge nearly twenty years later. Gary Ridgway, a truck painter, was known to it early. In 1987, acting under a warrant, investigators collected a saliva sample from him, which KUOW later called "the one thing to later prove Ridgway’s connection." At the time it connected him to nothing.
Dave Reichert, one of the original detectives, became sheriff in 1997 and reopened the case. In 2001 the forensic scientists Beverly Himick and Jean Johnston of the Washington State Patrol Crime Laboratory, working with the improved testing of the day, linked Ridgway’s DNA to several of the killings, the prosecutor Jeff Baird later told the American Academy of Forensic Sciences. Ridgway was arrested on November 30, 2001. The Everett Herald, reporting for the Associated Press, said the DNA matched evidence from three of the earliest victims. He was charged with four counts of aggravated first-degree murder.
DNA alone could not carry the rest. Baird wrote that, even after extensive testing, "no physical evidence whatsoever" linked Ridgway to most of the victims. In 2003 the forensic microscopist Skip Palenik of Microtrace reported tiny spheres of sprayed paint on evidence from several cases and on items seized from Ridgway in the 1980s, and three more counts followed. On November 5, 2003, under an agreement in which King County Prosecuting Attorney Norm Maleng gave up the death penalty in return for a full accounting of the killings, Ridgway pleaded guilty to 48 counts of aggravated first-degree murder. On December 18 Judge Richard Jones sentenced him to 48 consecutive life terms. He pleaded guilty to a 49th count in February 2011. Asked by Reichert what a book on the case should be called, Ridgway suggested "Technology Caught the Green River Killer," KUOW reported.
By the early 2000s the offender data bank had become the point of the exercise. In 2002 Chester Dewayne Turner pleaded no contest to a sexual assault in Los Angeles and, under the plea, gave a DNA sample, which was entered into law enforcement databases, the Associated Press reported. California’s CODIS system matched his reference sample to the 1998 killing of Paula Vance, according to the Los Angeles Police Department, which had retested older evidence that had once been typed only for blood group.
The department’s cold case homicide unit had six detectives and a backlog of thousands of killings. Detectives Cliff Shepard and Jose Ramirez compared Turner’s profile with evidence kept from other unsolved deaths of women in South Los Angeles, and on October 23, 2004, the LAPD announced that DNA linked him to 13 murders between 1987 and 1998. It called him "the most prolific serial killer ever identified in the history of the City of Los Angeles." Chief William J. Bratton cited the case in promoting Proposition 69, a measure on the November 2004 ballot to take DNA from people arrested for felonies.
The same comparisons undid a conviction. In 1995 a Los Angeles jury had convicted D.A.J., a janitor with an intellectual disability, of murder and manslaughter in the deaths of three women in 1992. In 2002 the Post Conviction Assistance Center was appointed to represent him under California’s new law allowing DNA testing after conviction. Two of the four evidence kits in his case had been destroyed; the two that survived excluded him and matched Turner. On March 4, 2004, D.A.J.'s convictions were vacated and he was released, the National Registry of Exonerations records. He later settled with the City of Los Angeles for 720,000 dollars.
A jury convicted Turner of ten first-degree murders in April 2007, and he was sentenced to death. The Supreme Court of California upheld that death sentence in November 2020. In 2014 he was convicted of four more murders, among them two of the deaths for which D.A.J. had been imprisoned, and received four further death sentences. In June 2024 the Salt Lake County District Attorney charged him with the 1998 killing of Itisha Camp in Salt Lake City, after a DNA profile developed years earlier was finally entered in the national index and matched him. That charge has not been tried.
Christine Eadie and Helen Scott, both 17 and both recently out of school, went out with friends in Edinburgh on the evening of October 15, 1977. Their deaths came to light in East Lothian the next day. For almost thirty years no one was charged. Forensic scientists kept the evidence. A first attempt to obtain DNA in 1988 failed because the technique was too new, the Edinburgh Evening News reported, and when a male profile was obtained in 1998, about 400 men were tested and every result was negative.
The man who would be convicted was already in prison. Angus Robertson Sinclair, a Glasgow man who had been sentenced to ten years' detention in 1961 for the culpable homicide of a seven-year-old girl, Catherine Reehill, had been serving a life sentence since 1982 for offenses against children. In 2001 advances in DNA work linked him to the 1978 murder of Mary Gallacher, a 17-year-old from Glasgow, and on June 4, 2001, a jury at the High Court in Glasgow convicted him. In April 2004 further work on the evidence kept from the 1977 case matched Sinclair, with odds of a billion to one.
He was tried in Edinburgh in 2007. On September 10, before the jury could consider a verdict, Lord Clarke upheld a submission of no case to answer, saying the Crown’s evidence could not overcome the absence of crucial forensic evidence, and acquitted him. The Lord Advocate, Elish Angiolini, told the Scottish Parliament that she would have appealed had the law allowed it. The Parliament then passed the Double Jeopardy (Scotland) Act 2011, which permits the High Court to set aside an acquittal where new and compelling evidence emerges.
The new evidence came from the forensic company Cellmark in 2011 and 2012. Using Crime-Lite, a light source that showed where material had been deposited and revealed traces invisible in ordinary light, its scientists obtained a full profile of Sinclair and further traces of his late brother-in-law, Gordon Hamilton, which the Crown argued tied both men to the killings themselves. It was the first use of the technique in a Scottish criminal case. "Without Crime-Lite, there would have been no trial two," the Lord Advocate Frank Mulholland said later. On March 27, 2014, three High Court judges set the acquittal aside, the first such order under the Act. On November 14, 2014, a jury at the High Court sitting in Livingston convicted Sinclair of both murders, with other charges, acting together with Hamilton, who had died in 1996 and was never tried. Lord Matthews imposed a punishment part of 37 years, described as the longest a Scottish court had set. Sinclair died at HMP Glenochil on March 11, 2019, aged 73, having admitted none of it.
Wendy Knell, 25, and Caroline Pierce, 20, lived less than a mile apart in Tunbridge Wells and did not know each other. Both were killed in 1987, Wendy in June and Caroline in November, and the press called the cases the Bedsit Murders. DNA profiling was too young to help. In 1999 detectives obtained a full DNA profile from the 1987 evidence, but it matched no one on the National DNA Database, which had been launched in 1995, ITV News reported.
The breakthrough came from the relatives of the people already on file. In 2019, after a partial profile linked the two killings forensically for the first time, Kent Police compared the profile against the national database for possible family members of the unknown man and drew up a list of about 1,000 names. The list was narrowed to about 90 people most likely to be close relatives, who were asked to give voluntary samples. In late November 2020 one came back as a very close match, and a comparison with the profile from the first case was exact. David Fuller, a hospital electrician living in Heathfield, East Sussex, was arrested in December 2020. "It’s him," scientists told Detective Chief Superintendent Paul Fotheringham while Fuller was in custody.
Partway through his trial at Maidstone Crown Court, on November 4, 2021, Fuller changed his pleas and admitted both murders. On December 15, 2021, Mrs Justice Cheema-Grubb imposed a whole life order. The investigation also exposed further offenses at two hospitals where he worked, to which he pleaded guilty, and led to an independent inquiry chaired by Sir Jonathan Michael.
California carried relative-matching into an American murder case first. Attorney General Jerry Brown adopted a familial DNA policy in April 2008 over strong opposition, limited to major violent crimes after other leads were exhausted. In 2009 a relative of Lonnie David Franklin Jr. was convicted of a felony weapons charge and his DNA entered the state data bank; within weeks a comparison pointed toward a family member of the unknown man behind a series of killings of women in South Los Angeles. The Spokesman-Review, carrying the Associated Press report, identified the relative as Franklin’s son. DNA from items Franklin discarded, collected by an undercover detective, then linked him directly. He was arrested on July 7, 2010. Brown said the arrest was "proof positive" that the method belonged in "law enforcement’s crime-fighting arsenal." On May 5, 2016, a jury convicted Franklin of ten murders and one attempted murder, and that August he was sentenced to death. He died at San Quentin State Prison on March 28, 2020.
Joseph James DeAngelo had never been required to give a sample to any criminal database, so no relative in one could point to him. In 2018 investigators instead uploaded a DNA profile, generated from evidence preserved since 1980, to genealogy services used by ordinary people tracing their families, and built family trees from the distant cousins who appeared. The work narrowed thousands of relatives to six men of the right age who had lived near the crimes, and then to one, a former police officer living in Citrus Heights, Sacramento County. He was arrested on April 24, 2018. On June 29, 2020, he pleaded guilty to 13 counts of first-degree murder and 13 counts of kidnapping to commit robbery, and admitted 161 uncharged crimes against 61 further victims; the Sacramento County District Attorney, Anne Marie Schubert, credited "the revolutionary tool of Investigative Genetic Genealogy." On August 21, 2020, he was sentenced to life without the possibility of parole. The technique moved faster than the rules. The United States Department of Justice issued an interim policy on forensic genetic genealogy that took effect on November 1, 2019, and in 2021 Maryland and Montana restricted police access to such databases, TechCrunch reported.
Set side by side, the cases trace the working life of a single idea. In Leicestershire it was used first to rule a man out, then to screen a population. In Virginia and New Brunswick it had to win admission in court, and the Canadian argument showed that the fight would come over statistics rather than the laboratory bench. Virginia’s legislature answered with an offender data bank in 1989, Britain launched its national database in 1995, and by 2001 a saliva sample collected in Washington in 1987 could do what it could not do when it was taken. In Los Angeles the data bank produced a name for thirteen killings and, through a new post-conviction testing law, freed a man imprisoned for some of them.
Each advance was matched by a legal change or a legal argument: the rejection of Frye in Virginia, the reasonable reliability test in Canada, double jeopardy in Scotland, the familial policy in California, federal and state rules on genealogy. The men who were cleared, R.B. in 1986, D.V. in 1989 and D.A.J. in 2004, are as much a part of the record as the men who were convicted. Alec Jeffreys’s own description of what he had made was the narrowest one available. It established whether sample X came from person Y. The village screen, the data bank, the list of a thousand relatives and the family tree were built by detectives around that one question.
• 1961: Angus Robertson Sinclair, 16, kills Catherine Reehill, 7, in Glasgow; sentenced on August 25, 1961, to ten years' detention for culpable homicide.
• October 1977: Christine Eadie and Helen Scott, both 17, are killed; their deaths come to light in East Lothian on October 16.
• 1978: Mary Gallacher, 17, is killed in Glasgow.
• 1982: Gary Ridgway’s killings in King County begin; Sinclair is sentenced to life for offenses against children.
• November 1983: Lynda Mann, 15, is killed in Narborough, Leicestershire.
• January 1984: Carolyn Hamm is killed in Arlington, Virginia; D.V. later enters an Alford plea and is sentenced to 35 years.
• September 10, 1984: Alec Jeffreys’s breakthrough at the University of Leicester.
• June 21, 1986: John Glendenning is killed at Black River Bridge, New Brunswick; police later take hair samples from Allan Legere.
• July 1986: Dawn Ashworth, 15, is killed in Enderby; DNA testing clears R.B. and shows one man killed both girls. A blood screen of about 5,000 local men follows, and a colleague gives a sample in Colin Pitchfork’s name.
• 1987: in King County, investigators collect a saliva sample from Ridgway.
• June and November 1987: Wendy Knell, 25, and Caroline Pierce, 20, are killed in Tunbridge Wells.
• September to December 1987: Debbie Dudley Davis, Dr. Susan Hellams, Diane Cho and Susan Tucker are killed in Virginia.
• January 20, 1988: Timothy Wilson Spencer is arrested in Richmond.
• January 22, 1988: Pitchfork is sentenced to life at Leicester Crown Court after guilty pleas.
• March 16, 1988: Lifecodes reports that Spencer’s DNA matches the Tucker, Davis and Hellams evidence.
• July 16, 1988: an Arlington jury convicts Spencer of capital murder and fixes a death sentence.
• January 4, 1989: Governor Gerald Baliles pardons D.V.
• 1989: the Virginia state laboratory begins DNA testing for law enforcement; Virginia creates a DNA data bank for convicted sex offenders (widened to all felons in 1990).
• May to November 1989: after Legere’s escape, Annie Flam, Donna and Linda Daughney and Father James Smith are killed in the Miramichi region; the RCMP confirms a DNA link on November 16; Legere is recaptured on November 24.
• September 22, 1989: the Supreme Court of Virginia upholds the Arlington and first Richmond judgments and the DNA evidence.
• April 22, 1991: the voir dire on DNA evidence in Legere’s case begins at Burton, New Brunswick.
• November 3, 1991: Legere is convicted of four counts of first-degree murder.
• April 27, 1994: Spencer is executed in Virginia.
• December 16, 1994: the New Brunswick Court of Appeal upholds the DNA evidence against Legere.
• 1995: Britain’s National DNA Database is launched.
• 1999: a full profile is obtained from the Tunbridge Wells evidence; it matches no one.
• June 4, 2001: Sinclair is convicted of the murder of Mary Gallacher.
• November 30, 2001: Ridgway is arrested after the 1987 saliva sample is matched.
• 2002: Chester Dewayne Turner gives a DNA sample after a no contest plea; D.A.J. is assigned post-conviction counsel for DNA testing.
• November 5, 2003: Ridgway pleads guilty to 48 counts of aggravated first-degree murder; sentenced on December 18.
• March 4, 2004: D.A.J.'s convictions are vacated and he is released.
• April 2004: DNA from the 1977 Edinburgh case is matched to Sinclair.
• October 23, 2004: the LAPD announces that DNA links Turner to 13 killings.
• April 2007: Turner is convicted of ten first-degree murders.
• September 10, 2007: Sinclair is acquitted on a submission of no case to answer.
• April 2008: California adopts a familial DNA policy.
• July 7, 2010: Lonnie Franklin Jr. is arrested after a familial match through his son.
• November 2011: the Double Jeopardy (Scotland) Act 2011 comes into force.
• March 27, 2014: the High Court sets aside Sinclair’s acquittal; on November 14 he is convicted.
• May 5, 2016: Franklin is convicted of ten murders; sentenced to death in August.
• April 24, 2018: Joseph James DeAngelo is arrested after a genetic genealogy inquiry.
• November 1, 2019: the US Department of Justice interim policy on forensic genetic genealogy takes effect.
• June 29, 2020: DeAngelo pleads guilty to 13 murders; sentenced on August 21 to life without parole.
• November 2020: the Supreme Court of California upholds Turner’s 2007 death sentence; a familial match in Kent points to David Fuller, who is arrested in December.
• November 4, 2021: Fuller pleads guilty to both 1987 murders; a whole life order follows on December 15.
• June 2024: Turner is charged in Utah with a 1998 killing.
• October 27, 2025: the Parole Board refuses Pitchfork’s release.
• March 9, 2026: Legere dies in custody at Edmonton Institution.