Some of the most famous cases solved with DNA evidence are also the cases that defined what forensic DNA can and cannot do: Colin Pitchfork’s 1988 conviction in England, Kirk Bloodsworth’s release from Maryland’s death row in 1993, Gary Ridgway’s arrest as the Green River Killer in 2001, and Joseph DeAngelo’s identification as the Golden State Killer in 2018. Each one changed the rules. And one lesser-known case, that of Lukis Anderson in California, changed them again by showing how a perfect DNA match can still point at the wrong person.
How a DNA Match Actually Identifies Someone
Everyone except identical twins carries a unique genetic code. Forensic scientists extract DNA from biological material left at a scene (blood, saliva, hair, skin cells) and build a profile that works like a biological fingerprint. Compared against a suspect’s sample or searched in a database, that profile either links a person to the crime or rules them out.
The database driving most of these matches in the United States is CODIS, the Combined DNA Index System, maintained by the FBI under the DNA Identification Act of 1994. As of late 2025 it holds more than 19.2 million offender profiles, 6.1 million arrestee profiles, and 1.4 million profiles from unsolved crime scenes, and has produced over 781,000 investigative hits.1Federal Bureau of Investigation. CODIS-NDIS Statistics Newer Rapid DNA instruments, authorized for booking-station use after the Rapid DNA Act of 2017, can produce a full profile from a cheek swab in one to two hours and search it against unsolved-crime profiles within a day.2Federal Bureau of Investigation. Rapid DNA Someone booked on a minor offense today could be tied to a decades-old sexual assault before making bail.
Colin Pitchfork, 1988: The First DNA Conviction
The first criminal conviction based on DNA evidence happened in England, and it made both of the technology’s uses visible on the same day. In 1983, 15-year-old Lynda Mann was raped and murdered near Leicester. Three years later, another girl, Dawn Ashworth, was killed under strikingly similar circumstances, and semen samples pointed to the same offender.3New England Journal of Medicine. DNA as Evidence – The Technology of Identification
Police had a suspect who had confessed to one of the killings. They took the crime scene evidence to Alec Jeffreys, a genetics professor at the University of Leicester who had recently developed what he called “DNA fingerprinting.” The suspect’s DNA did not match. He was innocent, and it was the first time DNA had ever cleared someone in a criminal case.4National Library of Medicine. Visible Proofs: Forensic Views of the Body – Alec Jeffreys and the Pitchfork Murder Case
With no suspect left, police asked all 5,000 men in the area to voluntarily give blood samples. A local baker named Colin Pitchfork paid a coworker to submit a sample under his name. When the coworker was overheard talking about the swap, police tested Pitchfork directly. His DNA matched both scenes, and he was convicted in 1988.3New England Journal of Medicine. DNA as Evidence – The Technology of Identification
Kirk Bloodsworth, 1993: The First U.S. Death Row Exoneration
In 1984, nine-year-old Dawn Hamilton was raped and murdered in Baltimore County, Maryland. Kirk Bloodsworth was convicted the following year, largely on eyewitness testimony, and sentenced to death. His conviction was overturned on appeal, but a second trial produced another conviction and two consecutive life sentences.
In 1992, Bloodsworth’s lawyers obtained court approval to test preserved biological evidence using a then-emerging technique called polymerase chain reaction, or PCR. His DNA did not match. After the FBI confirmed the result, he was released on June 28, 1993, the first person in the United States exonerated from death row by DNA evidence. He had spent nearly nine years in prison. The crime scene DNA was later matched through CODIS to Kimberly Shay Ruffner, who was already serving time for another offense.
Bloodsworth’s case turned out to be one of a pattern. More than 450 people in the United States have since been exonerated through DNA testing, and more than 100 of those cases involved false confessions in which innocent people gave up details prosecutors argued only the real offender could have known. Those details were unreliable. The accumulation of these cases has forced courts and police to reconsider how they weigh eyewitness identifications and confessions.
Gary Ridgway, 2001: A Cold Case Reopened by Better Technology
Gary Ridgway killed dozens of women in the Seattle area during the 1980s, dumping bodies along the Green River and in wooded areas south of the city. He was a suspect as early as 1984, and investigators took a saliva sample from him in 1987, but the DNA techniques of the time could not produce a definitive match. The investigation stalled for years.
In 2001, improved forensic DNA analysis let scientists match Ridgway’s saliva to sperm recovered from victims found in 1982 and 1983. He was arrested that November. To avoid the death penalty, he eventually confessed to 48 murders and led detectives to four previously undiscovered burial sites. In 2003 he pleaded guilty and received 49 consecutive life sentences without parole. The case is the standard argument for preserving biological evidence: a sample that means nothing in one decade can close the case in the next.
Joseph DeAngelo, 2018: The Golden State Killer and Genetic Genealogy
Joseph DeAngelo committed a series of rapes, burglaries, and murders across California from the mid-1970s through the mid-1980s. Investigators had a crime scene DNA profile but no match in CODIS, and the case sat cold for decades.
In 2018, investigators tried something new. They uploaded the crime scene profile to GEDmatch, a free public database where people share genetic data from consumer testing companies to find relatives. A genealogist used matches with distant relatives of the unknown offender to build a family tree and narrow the pool to DeAngelo.5Science. We Will Find You DNA Search Used to Nab Golden State Killer Can Home in on About 60% of White Americans Detectives then collected DNA from items DeAngelo discarded in public, and it matched the crime scene. He was arrested in April 2018. In 2020 he pleaded guilty to 13 counts each of murder and rape covering 161 crimes against 48 victims, and received 11 consecutive life sentences.
The technique, now called forensic genetic genealogy, worked, but it drew immediate backlash. GEDmatch users had uploaded their data to find distant cousins, not to help police. The site changed its terms of service and opted all users out of law enforcement searches by default, requiring anyone willing to participate to opt back in. The Department of Justice issued an interim policy restricting federal agencies and federally funded investigators from using genetic genealogy unless traditional methods have been exhausted, the case involves a violent crime such as murder or sexual assault, and a prosecutor has approved the search.6National Center for Biotechnology Information. Forensic Genealogy, Bioethics and the Golden State Killer Case
Lukis Anderson, 2012: When a Perfect Match Is Wrong
Not every famous DNA case is a triumph. In 2012, Lukis Anderson, a homeless man in San Jose, California, was arrested for murder after his DNA was found under a homicide victim’s fingernails. The evidence looked overwhelming. But Anderson had an airtight alibi: hospital records showed he had been admitted for severe alcohol intoxication hours before the killing and had stayed in bed through the night.
Investigators eventually worked out how his DNA got there. The same paramedics who had treated Anderson earlier that evening responded to the murder scene hours later. His DNA had likely transferred through medical equipment, possibly a pulse oximeter clipped to both patients’ fingers. He was cleared, but only after months in jail on a murder charge.
Modern forensic techniques are sensitive enough to pick up trace amounts of DNA from shed skin cells, and that sensitivity creates the problem. Research has shown DNA can move indirectly through shared surfaces, clothing, and laundry, and can pass through as many as six transfers from its original source. Mixed samples make it worse: when analysts try to separate DNA from multiple contributors on a single object, the risk of a false positive grows with each additional contributor, and accuracy drops further when the contributors come from populations with lower genetic diversity.7OregonNews. Limits of Forensic DNA Analysis A DNA match at a scene proves your genetic material was there. It does not, by itself, prove you were.
When Police Can Collect Your DNA Without a Warrant
The cases above prompt a fair question about the front end of the process: when can the government take your DNA in the first place? The Supreme Court answered that in 2013 in Maryland v. King, ruling 5–4 that police may take a cheek swab from anyone arrested for a serious offense as part of routine booking, the same way they take fingerprints and photographs.8Legal Information Institute. Maryland v. King You do not need to be convicted. An arrest supported by probable cause for a qualifying offense is enough for your profile to be uploaded to CODIS. If the charges are later dropped or you are cleared, most jurisdictions have expungement procedures, but the burden is on you to request removal.9Federal Bureau of Investigation. CODIS and NDIS Fact Sheet