Investigative genetic genealogy compares DNA from a crime scene with consumer DNA profiles to identify an unknown person’s relatives. Building family trees from those matches can solve old cases, but it raises serious privacy questions.
The technique in plain terms
Investigative genetic genealogy, often shortened to IGG, combines forensic science with family-history research. Investigators take DNA left at a crime scene, or recovered from unidentified human remains, and turn it into a profile that can be compared with profiles uploaded by members of the public to genealogy databases. The aim is not usually to find the person who left the DNA. Instead, investigators look for relatives such as distant cousins, who share some segments of DNA with the unknown person.
Genealogists then work outward from those relatives. Using birth, marriage and death records, census entries, newspaper archives and similar material, they build family trees and narrow down where the unknown person might sit within them. Police treat the result as an investigative lead rather than proof. A suspect identified in this way is normally confirmed through a conventional forensic comparison with a fresh DNA sample.
The BBC reports that the method can help track down offenders in cold cases, while also raising concerns about privacy. Both sides of that point are central to understanding the technique.
Origins in consumer genealogy
The method grew out of the consumer DNA testing market. Commercial companies began selling home test kits that let people learn about their ancestry and find relatives. Some customers then downloaded their raw genetic data and uploaded it to third-party sites that allowed comparisons across different testing companies. Those open databases became the foundation for IGG.
Adoptees and people looking for unknown biological parents had already developed many of the research methods used today. Volunteer genealogists showed that a handful of cousin matches, combined with thorough documentary research, could often identify a parent. Investigators and forensic genealogists then applied the same reasoning to crime scene samples and to unidentified remains.
The approach became widely known when US authorities used it to identify suspects in long-unsolved violent crimes. That publicity led to a quick expansion in its use, and to public debate about whether users of genealogy sites had agreed to their data being searched by police.
How the process works today
The typical workflow has several stages. First, a laboratory extracts DNA from the evidence. Standard police DNA databases use a small number of markers known as short tandem repeats. These are useful for direct matching but say little about distant relationships. For IGG, laboratories instead produce a profile of hundreds of thousands of single nucleotide polymorphisms (SNPs), the type of data generated by consumer ancestry tests. Old, degraded or very small samples can make this difficult, and whole-genome sequencing is sometimes used to recover enough usable data.
Second, the profile is uploaded to a genealogy database that allows law enforcement comparisons. Services such as GEDmatch and FamilyTreeDNA have policies under which users can choose whether their profiles may be compared with forensic samples. The largest consumer testing companies generally say they do not allow police searches without legal process.
Third, the database returns a list of people who share DNA with the sample, with an estimate of how much they share. The amount shared gives a rough idea of how closely related two people are.
Fourth, genealogists build family trees for the strongest matches, looking for points where the trees meet. This can take days or many months, depending on how close the matches are and how good the records are.
Finally, once a likely candidate has been identified, police use ordinary investigative methods. This may include collecting discarded items to obtain a DNA sample for direct comparison. Rules on how and when the technique may be used differ between countries. In the United States, the Department of Justice has issued an interim policy that limits federal use mainly to serious violent crimes and identifying human remains. The rules and practice in other countries, including the UK, are less settled, and the details of any particular force’s use are not always made public.
Common misunderstandings
One frequent misunderstanding is that IGG searches the main police DNA database. It does not. National forensic databases hold profiles from people who have been arrested or convicted. IGG depends on voluntary consumer data, much of it from people who have never had any contact with the police.
A second is that a database match identifies the offender. A match usually points to a relative, often a distant one. The identification comes from the genealogical research that follows, and it must be confirmed independently.
A third is that only people who upload their DNA are affected. Because relatives share DNA, one person’s upload reveals information about parents, siblings, children and cousins who never consented. This is the core of the privacy concern the BBC describes. Researchers have argued that once enough of a population has uploaded DNA, many people could be traced through relatives’ data whether or not they have tested themselves.
A fourth is that the method is infallible. Errors in family records, undisclosed adoptions, misattributed parentage and mistakes in building trees can all lead investigators towards the wrong person. That is why confirmatory testing matters. There are also concerns about transparency, because defendants and the public may not always learn how a lead was generated.
Lastly, some assume that opting out removes all risk. Opting out limits how a person’s own profile is used, but it cannot stop relatives from opting in. Database policies can also change over time.
Where to look next
Anyone who wants to understand the subject further should start with the terms of service and privacy policies of genealogy and DNA testing companies, which set out whether and how law enforcement may access user data. Government policy documents, such as the US Department of Justice’s interim policy, show how authorities have tried to limit the method’s use. In the UK, the bodies that oversee biometrics and forensic science are the relevant place to follow any regulation.
Academic work in bioethics, law and population genetics covers questions of consent, the effects on relatives, and how quickly identification becomes possible as databases grow. Court rulings and legislative debates show how judges and lawmakers are dealing with the technique. Mainstream reporting, such as the BBC’s coverage, explains how the method is used in particular investigations.
Frequently asked questions
What is investigative genetic genealogy?
Investigative genetic genealogy is a technique that compares DNA from a crime scene or unidentified remains with profiles in public genealogy databases. Investigators look for relatives of the unknown person, then build family trees from historical and public records to narrow down who that person might be. The result is treated as a lead, and police normally confirm it with a separate, conventional DNA comparison.
Can police see my DNA if I used an ancestry test?
It depends on the company and your settings. Some genealogy databases let users choose whether their profile can be compared with forensic samples, while the largest testing companies generally say they require legal process before sharing data. Even if you opt out, relatives who opt in may share enough DNA with you to help investigators trace you indirectly.
How is this different from the police DNA database?
Police DNA databases hold a limited number of markers from people who have been arrested or convicted, and are mainly used for direct matches. Investigative genetic genealogy uses much denser genetic data from consumer tests, uploaded voluntarily by the public, and works by finding relatives rather than the person themselves.
Is investigative genetic genealogy accurate?
The genetic comparisons are generally reliable at estimating relationships, but the overall process depends on human research. Incorrect family records, unknown adoptions or misattributed parentage can send investigators in the wrong direction. For this reason the technique produces leads, and a suspect should be confirmed by direct DNA comparison before any conclusion is drawn.
Why does genetic genealogy raise privacy concerns?
DNA is shared within families, so one person’s decision to upload a profile exposes information about relatives who never agreed to it. Critics also worry about transparency, possible expansion to less serious crimes, and changes to database policies. Supporters point to solved cases and identified remains, which makes the balance between public safety and privacy contested.
Sources and further reading
- BBC News technology coverage reporting on genetic genealogy in cold case investigations and the privacy concerns it raises
- US Department of Justice interim policy on the use of forensic genetic genealogy in federal investigations
- Published privacy policies and terms of service of genealogy databases and consumer DNA testing companies
- Peer-reviewed literature in bioethics, forensic science and population genetics on consent and relative-based identification
Surfaced from the rss:bbc_tech signal “DNA genealogy in policing”. AI-assisted draft, editorially reviewed.
