Forensic Genetic Genealogy, Explained Without the TV Hype
Forensic genetic genealogy, usually shortened to FGG or FIGG, is a way to generate investigative leads from crime-scene DNA when standard forensic DNA methods have not identified anyone. The cleanest official description comes from the U.S. Department of Justice and the National Institute of Justice: investigators first try the usual route through STR DNA and CODIS; if that fails, they may use a different kind of DNA profile based on hundreds of thousands of SNPs and combine it with traditional genealogy research to look for relatives of the unknown person.
That sounds dramatic, but it is much less magical than television makes it look. FGG does not usually spit out a suspect’s name in one click. It more often finds distant relatives, then requires a genealogist to build family trees, narrow branches by age, sex, geography, and case facts, and only then suggest possible identities for police to investigate. The National Academies described it in 2024 as a multistep, multidisciplinary process that combines advanced DNA analysis, genealogy databases, and conventional records research to generate leads for previously unknown DNA samples.
What it is not
It is not the same thing as a normal CODIS hit. CODIS is a law-enforcement DNA system built around STR markers and known offender or forensic profiles. FGG uses a different style of DNA data and searches genealogy-style databases instead. DOJ’s policy is explicit that information derived from FGG is not uploaded into CODIS, and NIJ’s explainer says CODIS is the first step precisely because FGG is the backup route when CODIS produces no useful match.
It is also not supposed to be “crime-scene DNA uploaded everywhere on the internet.” DOJ says FGG profiles may be searched only in genealogy services or open-data databases that explicitly notify users and the public that law enforcement may use the service for crime investigations or unidentified human remains cases. GEDmatch’s own 2024 terms likewise say law-enforcement uploads must go through GEDmatch PRO and may be used to identify perpetrators of certain violent crimes or to identify human remains.
And it is not an arrest tool by itself. DOJ says plainly that a suspect shall not be arrested based solely on a genetic association from a genealogy service. Once investigators identify a possible person, they still need ordinary police work and then a direct STR comparison between the suspect’s DNA and the original forensic profile to confirm that the crime-scene DNA could have come from that person.
How the process actually works
The real process is slower and more procedural than TV suggests.
A usable forensic sample is collected from a crime scene or from unidentified remains. A lab first develops the usual forensic DNA profile and runs it through CODIS. If CODIS fails to identify a known person, investigators may consider FGG. At that point, a lab or vendor generates an SNP-based profile, which is the kind of data consumer genealogy systems use to estimate relatedness. That profile is then searched in an approved genealogy database to find people who share DNA segments with the unknown sample. Those people are usually not suspects. They are relatives of the unknown person, sometimes fairly distant ones. A genealogist then builds family trees forward in time until one or more possible identities fit the case. Only after that does traditional investigation resume.
The National Academies’ 2024 workshop summary puts it well: an approved database is searched for people who share DNA with the unknown profile, and those hits become starting points for family-tree building. It also notes that only a small percentage of all consumer DNA samples are actually available to law enforcement for this purpose. So even though millions of people have tested with consumer services, the searchable universe for FGG is narrower than many people assume.
Why it works at all
FGG works because relatives share chunks of DNA. DOJ’s policy explains that genealogy services report a genetic association based on how much DNA two profiles share, usually measured in centiMorgans. In general, more shared DNA suggests a closer relationship. But this is where a lot of public confusion starts: a match in FGG usually means “this unknown person may be related to this database user,” not “this database user is the suspect.”
That is why genealogical research is the heart of the method. DNA alone often gets you into the right extended family. Records work, obituaries, censuses, public documents, age filtering, geography, and case facts are what narrow that family down to a realistic candidate. The “breakthrough” people hear about in news coverage is often the end result of weeks or months of tree-building, not just a database match.
When police are supposed to use it
Under DOJ’s policy, FGG is meant mainly for unsolved violent crimes and for identifying unidentified human remains believed to involve homicide. The policy says agencies may consider FGG when the case involves an unsolved violent crime and the sample is reasonably believed to come from a putative perpetrator, or when the remains are reasonably believed to be those of a suspected homicide victim. It also allows some use in other violent crimes presenting a substantial and ongoing threat to public safety or national security, but the baseline category is serious violence.
The same policy also says CODIS must be tried first and that investigators must have pursued reasonable investigative leads before moving to FGG. In other words, this is supposed to be a later-stage tool, not the first thing police reach for.
The rules are not one single national rulebook
This is where many summaries go wrong. There is no single all-purpose American FGG law that binds every police department in the same way.
There is a federal DOJ policy, but it applies to DOJ components and to agencies using DOJ funding or DOJ-linked resources. It is important, but it is still a policy framework, not a universal statute. The National Academies’ 2024 workshop noted that states differ, and pointed to Maryland as the first state to enact a law specifically regulating forensic investigative genetic genealogy.
Maryland’s updated 2025 law is a good example of how state rules can be more specific. It defines FGG as SNP-based analysis plus a search in a public genomics database or direct-to-consumer genealogy service plus genealogical research, and it requires judicial authorization before FGG starts. It also requires that the perpetrator’s identity be unknown, that the case involve murder, rape, a felony sexual offense, or a substantial ongoing public-safety or national-security threat, and that an STR profile already be developed and searched in the state and national DNA databases without identifying a known individual. The amended law takes effect October 1, 2025.
So when someone asks for the “rules,” the honest answer is: there are federal policy rules, database terms-of-use rules, and sometimes state-specific legal rules layered on top of each other.
Privacy guardrails, at least on paper
DOJ’s policy tries to build in privacy limits. It says investigative agencies must identify themselves as law enforcement when using genealogy services, may search only services that clearly tell users law enforcement may be present, and must use profiles only for law-enforcement identification purposes. It also says FGG data cannot be used to determine a person’s predisposition for disease, medical condition, or psychological trait.
The policy also addresses third-party relatives. If investigators want to collect a reference sample from someone who is not a suspect but may be genetically closer to the unknown person than the database match, they are supposed to seek informed consent first. If they believe asking would compromise the investigation, they may covertly collect the sample only with prosecutor approval, and a search warrant is required before a vendor lab performs FGG analysis on a covertly collected third-party reference sample.
There are disposal rules too. DOJ says that if FGG does not lead to an arrest and charges, agencies should promptly destroy third-party reference samples, derivative FGG profiles, and associated genealogy-service account information and data after the investigative use is complete. If there is a prosecution, destruction is tied to later judicial process.
Where the privacy debate really sits
The real debate is not whether FGG can work. It plainly can. The debate is about scope, consent, and mission creep.
The National Academies’ 2024 workshop emphasized the need for standards, regulation, and public trust, and noted that only a small portion of consumer-DNA profiles are available to law enforcement. That sounds reassuring, but it also highlights the core tension: people upload DNA for family research, and some subset of those uploads may later become useful in criminal investigations involving relatives they do not know about.
Database terms matter a lot here. GEDmatch’s current terms say law-enforcement uploads for violent crimes or human remains must go through the dedicated GEDmatch PRO portal, not the public site, and community-safety materials say law enforcement can see limited matching information rather than everyone’s raw DNA files. Even so, the fact that database policies can change over time is one reason critics want more statutory guardrails rather than relying only on private terms of service.
Why TV gets it wrong
TV usually makes FGG look like a futuristic identification machine. In practice, it is closer to a lead-generation system built on relatives.
It depends on whether a usable forensic sample exists. It depends on whether CODIS failed first. It depends on whether a searchable genealogy database has usable relatives in it. It depends on whether the SNP profile is good enough. It depends on whether a genealogist can build the right family tree. And even then, it still ends with conventional police work and confirmatory STR testing.
So the simplest non-hyped description is this: forensic genetic genealogy is a way to turn unknown DNA into a family-tree clue. It is powerful, but it is not instant, not universal, and not self-proving. It is also tightly entangled with privacy and consent questions because it works by leveraging relatives, not only the person who left the crime-scene DNA.
The clearest way to think about it
Think of FGG as sitting between forensic lab science and old-fashioned investigation.
The science side builds a genealogy-compatible DNA profile and finds genetic associations. The human side does the rest: build trees, compare ages, locations, sex, timelines, and case facts, then test whether the likely person truly matches the original forensic evidence. That is why DOJ says FGG is an investigative lead tool, not a stand-alone proof engine.
That also explains why the method inspires both hope and unease. It can help identify violent offenders and unknown remains when traditional methods stall. But it also forces law enforcement, courts, labs, and the public to answer a difficult question: how much investigative power should flow from DNA that relatives voluntarily uploaded for entirely different reasons?
