Solving Crimes with DNA

On a spring morning in 2018, police surrounded a small home in Citrus Heights, California. The man they arrested, Joseph James DeAngelo, was a former police officer who had been living a quiet life as a grandfather. To his neighbors, he was a grumpy retiree who tinkered with his boat. To investigators, he was the Golden State Killer, a man who had eluded capture for over forty years, leaving behind a trail of murders and assaults across California. What finally gave him away wasn’t a confession or a witness—it was DNA. A few microscopic samples collected decades earlier and compared to a distant cousin’s genealogy test cracked one of the most notorious cold cases in American history.

That arrest stunned the world and made headlines everywhere. It was a vivid demonstration of something investigators had known for years: forensic DNA is one of the most powerful tools in modern policing. It has reshaped criminal justice, solving cases that once seemed unsolvable and freeing those who were wrongfully accused. Yet behind this incredible technology is a fascinating story of scientific discovery, meticulous detective work, and difficult conversations about privacy and ethics.

From Scientific Breakthrough to Crime-Solving Tool

The idea of using DNA to identify people was unheard of until the 1980s. In 1984, British geneticist Alec Jeffreys discovered in a University of Leicester lab that certain regions of DNA contained repeating sequences unique to each individual. He realized these sequences could act like a biological fingerprint, identifying a person with astonishing precision.

Two years later, that insight changed the course of a murder investigation in a small English village. Two teenage girls had been killed, and a local man confessed to one of the crimes. But when police tested his DNA against samples collected from both victims, he was cleared completely. The real killer, Colin Pitchfork, was caught soon after, becoming the first person convicted on the strength of DNA evidence. This was the moment that DNA shifted from a scientific curiosity to a groundbreaking investigative tool.

Inside the Lab: Turning Cells into Clues

Forensic DNA analysis may sound like magic, but it’s a careful, multi-step process. Investigators first collect biological material from a crime scene—blood, hair, saliva, or even skin cells invisible to the naked eye. In the lab, technicians extract the DNA and measure its quality, because crime scene samples are often degraded or contaminated. Using a technique called polymerase chain reaction, or PCR, they make millions of copies of the DNA to ensure there’s enough to analyze.

Analysts then examine specific locations on the DNA known as short tandem repeats (STRs). These sequences vary widely between individuals, and the combination of several STR markers creates a DNA profile that is effectively unique. This profile can be compared to suspects’ samples or checked against massive databases like CODIS, the FBI’s Combined DNA Index System. A match can link a person to a crime scene—or, just as importantly, clear them entirely.

When a crime scene DNA profile is used, investigators may find a genetic match with a distant relative of the suspect, meaning the DNA at the crime scene belongs to a genetic cousin of a match in a DNA database. Forensic genealogists then use that match as a starting point to find which of their genetic cousins left the DNA behind at the crime scene, tracing family trees with public records, obituaries, and historical documents to map relationships and identify possible suspects. Once they narrow down candidates, investigators collect traditional evidence—like discarded items—to confirm a direct DNA match. This step-by-step process transforms a single distant match into a concrete lead, often solving cases that have been cold for decades. It’s a combination of advanced science, genealogy expertise, and classic detective work.

The Genealogy Revolution

One of the most dramatic shifts in forensic science has been the rise of genetic genealogy. Traditionally, DNA evidence from a crime scene could only be matched against samples in law enforcement databases, like CODIS, which holds DNA profiles from convicted offenders, arrestees, and some crime scenes. If a suspect wasn’t already in the system, investigators often hit a dead end. Genetic genealogy changed that. Instead of looking only for exact matches, investigators now look for partial matches or shared stretches of DNA that indicate family relationships.

Here’s how it works: investigators take a DNA profile from a crime scene and upload it to public genealogy websites that allow law enforcement searches, such as GEDmatch or FamilyTreeDNA. These sites were originally designed for people curious about their ancestry or looking for relatives, but they’ve become invaluable tools for solving crimes. When a crime scene sample is uploaded, the site compares the sample against its database and identifies users who share genetic material with the unknown suspect. These relatives could be as close as a sibling or as distant as a fourth cousin. From there, genealogists step in. They analyze family trees, historical records, and other documents, piecing together relationships until they narrow down potential suspects. In many cases, they create elaborate family maps, tracing generations of relatives until a likely candidate emerges—someone whose age, location, and other circumstances align with the crime.

This method has completely changed cold-case investigations. Since the Golden State Killer was identified in 2018, investigative genetic genealogy has been credited with solving over 500 cases, many of which had been stalled for decades. It’s especially powerful in cases where traditional evidence is scarce, because even a distant family match can provide a starting point. Law enforcement agencies now work closely with professional genealogists who specialize in criminal cases, combining DNA science with old-fashioned detective work. In fact, a growing field of forensic investigative genetic genealogy (FIGG) has emerged, with its own training programs, ethical guidelines, and certification standards.

But while the successes are remarkable, the field is also under close scrutiny. Privacy concerns are front and center because users of genealogy websites often upload their DNA for recreational purposes without realizing it might be used in a criminal investigation. Following the Golden State Killer case, GEDmatch changed its policies to require users to “opt in” if they want their DNA to be available to law enforcement searches. FamilyTreeDNA also allows law enforcement access but under specific guidelines. Despite these restrictions, thousands of users have opted in, and investigators now see genetic genealogy as a crucial tool in tackling unsolved crimes, particularly murders and sexual assaults. What was once a fringe technique is quickly becoming standard practice in cold-case work, bridging the gap between cutting-edge science and traditional detective work.

DNA Gets Faster and Smarter

In the early days of DNA profiling, a single test could take weeks. Today, rapid DNA machines can process a sample in under two hours, allowing police to quickly check arrestees against databases. Another advancement, called touch DNA, can extract genetic material from just a few cells left on a surface. This technology has cracked cases that once seemed hopeless, though it comes with challenges: detecting DNA doesn’t always prove someone’s involvement in a crime, especially in public spaces where DNA can transfer easily.

Scientists are pushing the boundaries even further. Some labs can now predict traits like hair and eye color from DNA samples, a technique called DNA phenotyping. Researchers are also exploring epigenetic markers that might estimate a person’s age or even their lifestyle habits. These methods are still developing, but they hint at a future where investigators could create a detailed profile of a suspect from a single drop of blood.

Why This Matters for Us

To help this cause, we can upload our DNA results to GEDmatch. Uploading your DNA to GEDmatch can directly help solve cold cases by giving investigators a starting point they wouldn’t otherwise have. When you upload your profile, GEDmatch compares your genetic markers to others in its database, identifying relatives—even distant cousins—of unknown suspects or unidentified victims. Trained genetic genealogists then build family trees from these connections, narrowing down identities that can lead to arrests or identifications. Many famous cold cases, like the Golden State Killer and the Buckskin Girl, were solved this way. Opting into law enforcement matching turns your interest in ancestry into a tool for good.

At Price Genealogy, we specialize in turning complex DNA evidence into clear, actionable answers. Whether you’re trying to solve a decades-old cold case, identify an unknown ancestor, or navigate the rapidly evolving world of genetic genealogy, our team has the expertise to guide you from start to finish. We combine cutting-edge forensic analysis with traditional genealogical research, ensuring that every lead is pursued with accuracy and care. From interpreting raw DNA data to building detailed family trees, Price Genealogy offers personalized, end-to-end support. Let us help you uncover the truth your DNA holds—because every strand tells a story.

James

Pictures:

1. DNA strand, public domain, https://unsplash.com/s/photos/dna
2. Smithsonian Institution Archives, Barbara McClintock (1902-1992) shown in her laboratory in 1947, public domain, https://commons.wikimedia.org/wiki/File:Barbara_McClintock_(1902-1992)_shown_in_her_laboratory_in_1947.jpg
3. Genealogy chart, public domain, https://unsplash.com/s/photos/genealogy

Sources:

1. Geary, L. “A Critical Eye Toward Commercial DNA Database Criminal Procedures.” University of Chicago Law Review Online. Accessed September 5, 2025. https://lawreview.uchicago.edu/online-archive/critical-eye-toward-commercial-dna-database-criminal-procedures.
2. Glynn, C. L. “The Emergence of Forensic Genetic Genealogy.” Journal of Law and the Biosciences 9, no. 1 (2022). https://pmc.ncbi.nlm.nih.gov/articles/PMC9407302/.
3. “Investigative Genetic Genealogy.” Wikipedia. Last modified December 2023. https://en.wikipedia.org/wiki/Investigative_genetic_genealogy.
4. “Investigative Genetic Genealogy: The Intersection of DNA and Genealogy.” Southern California University of Health Sciences. Accessed September 5, 2025. https://www.scuhs.edu/mshgg/investigative-genetic-genealogist/.