Investigative Genetic Genealogy: DNA, Databases, and Rules

Investigative genetic genealogy is a method law enforcement uses to identify unknown suspects and unidentified human remains by comparing crime scene DNA against profiles that private individuals have voluntarily uploaded to consumer genealogy databases, then building family trees from the resulting partial matches until the work points to a specific person. It is reserved for serious violent crimes and unidentified remains cases, and any identification it produces must be confirmed by a traditional DNA comparison before an arrest can proceed.¹

The technique rose to public attention in 2018 after investigators used it to identify a suspect in the Golden State Killer case.² Since then it has generated leads in hundreds of cold cases, and a federal interim policy together with a growing set of state laws now define the rules agencies have to work within.

Which Cases Qualify

Federal policy restricts the technique to serious violent crime. The Department of Justice defines “violent crime” for these purposes as any homicide or sexual offense. A prosecutor can also authorize use for other violent crimes when the circumstances present an ongoing threat to public safety or national security. Identifying unidentified human remains, including suspected homicide victims, also qualifies.¹

Before an agency can turn to genealogy, it has to upload the forensic DNA profile to the Combined DNA Index System (CODIS) and get no match. This is a hard prerequisite. The rule exists to keep agencies from bypassing the national criminal database, which is faster, cheaper, and less invasive. Only when CODIS fails does the door open to genealogical searching.¹

In practice that means the technique is reserved for cases where no known offender profile exists in any criminal database. Usually those are cold cases, sometimes decades old, where the perpetrator was never arrested for a qualifying offense or no suspect was ever developed.

How the Process Actually Works

Standard forensic DNA testing and genetic genealogy use fundamentally different types of markers, so a CODIS-compatible profile cannot be reused for genealogical searching. CODIS examines 20 specific locations in the genome using Short Tandem Repeats (STRs), which produces a profile designed for direct matching: this crime scene sample came from this person.³ Genealogy requires Single Nucleotide Polymorphism (SNP) analysis, which reads hundreds of thousands of markers across the whole genome. That broader dataset reveals family relationships rather than just confirming identity.⁴

Labs generate SNP profiles through whole genome sequencing or SNP microarray technology. Both produce a digital data file containing the raw genetic information needed for comparison against genealogical databases. Sample quality drives everything. Blood or saliva is straightforward. Degraded material from an old crime scene requires specialized extraction and costs more.

Recent research funded by the National Institute of Justice has expanded what counts as a usable sample. Investigators demonstrated that as little as five centimeters of rootless hair can yield enough DNA for genetic genealogy analysis with greater than 99 percent allele-call accuracy, matching the reliability of deep sequencing from saliva. The technology has been commercialized and is in active forensic use, which matters for cold cases where a rootless hair on clothing may be the only biological evidence that survived.⁵

Searching the Databases

With a digital SNP profile in hand, investigators upload it to a genetic genealogy database that permits law enforcement searches.⁶ The database identifies matches based on shared centimorgans, a unit measuring the length of identical DNA segments inherited from a common ancestor. More shared centimorgans means a closer relationship.⁴ Close matches are rare. Forensic genealogists usually work with partial matches from second, third, or even fourth cousins, where the shared DNA is measured in the low hundreds of centimorgans.

Building the Family Tree

From those partial matches, a forensic genealogist identifies the most recent common ancestor shared by several different users who matched the unknown profile. The genealogist then builds family trees forward from that ancestor through subsequent generations using census records, marriage certificates, obituaries, and other public records. The work narrows systematically from distant cousin branches toward a specific individual whose age, location, and life history fit the facts of the case. This phase is labor-intensive and can take weeks or months, depending on how distant the closest match is and how well-documented the relevant family lines are.

Confirming the Suspect

A genealogy match is an investigative lead, not probable cause. DOJ policy is explicit that no one can be arrested based solely on a genetic association generated by a genealogy service. A direct STR comparison between the suspect’s DNA and the crime scene evidence is required first.¹

Investigators obtain that reference sample most often through what detectives call a “trash pull,” collecting a discarded cup, water bottle, or cigarette butt from a public location. The DOJ policy requires prosecutor concurrence before executing this kind of covert collection, and detectives apply full chain-of-custody protocols. The lab then runs an STR comparison between the abandoned sample and the original crime scene evidence. If those 20-marker profiles match, the result provides the probable cause for a judge to issue an arrest warrant.¹ The arrest never rests on inferred family relationships. It rests on a direct biological match.

Which Databases Participate

Only two major platforms permit law enforcement searches, and both require individual users to affirmatively opt in. No one’s data is searchable by default.

GEDmatch, acquired by the forensic genomics company Verogen, offers four privacy tiers. Only users who select the “Opt-in” category have their DNA compared against uploads made by or on behalf of law enforcement for violent crime investigations. Users who select “Opt-out” are still matched for unidentified human remains cases but not for suspect identification.⁷ FamilyTreeDNA takes a similar approach: law enforcement agencies must create dedicated accounts, searches are restricted to qualifying violent crime or unidentified remains cases, and users must opt in to Investigative Genetic Genealogy Matching.⁸

The larger consumer testing companies do not participate. 23andMe, which filed for bankruptcy and was sold to a nonprofit in 2025, has consistently refused to release individual customer data to law enforcement without the customer’s explicit consent. Across 11 total law enforcement requests received through early 2025, the company produced customer data zero times.⁹ Ancestry has similarly declined to allow law enforcement searches of its database. The pool of searchable profiles is a fraction of the total consumer DNA testing market.

The Federal Rules: DOJ’s Interim Policy

The Department of Justice issued its Interim Policy on Forensic Genetic Genealogical DNA Analysis and Searching in 2019, and it remains the controlling federal framework. Despite being labeled “interim,” the policy has not been finalized, updated, or replaced.¹⁰ It applies to all DOJ components and to state and local agencies using federal resources for these investigations. The core requirements:

CODIS first. The forensic profile must be uploaded to CODIS and return no match before genetic genealogy can be attempted.
Violent crimes only. Searches are limited to homicides, sexual offenses, and other violent crimes where a prosecutor authorizes the use and the circumstances present an ongoing threat to public safety.
Investigative lead only. Results cannot serve as probable cause for an arrest or search warrant. A direct STR comparison is required.
Prosecutor concurrence. A prosecutor must approve the plan before detectives covertly collect reference DNA from a suspect or third party.
Data destruction. If the investigation does not result in an arrest, the agency must destroy all genetic profiles, genealogy service account data, and third-party reference samples, then document the destruction.¹

The policy’s reach is narrower than many assume. It governs federal investigations and federally funded work. It does not bind state or local agencies operating independently with their own resources, though many follow it voluntarily as a best-practices framework.

State Laws

A small but growing number of states have enacted their own statutes. The earliest and most detailed laws require judicial authorization before investigators can search consumer DNA databases, restrict searches to violent crimes, require CODIS to be exhausted first, mandate data destruction after the investigation closes, and impose licensing requirements on the labs and genealogists performing the work. Some go further by prohibiting covert DNA collection from third parties who have declined to provide a sample voluntarily and by creating criminal penalties for violations.

Other states have approached the issue through broader genetic privacy legislation regulating how direct-to-consumer testing companies handle law enforcement requests. Some permit disclosure with valid legal process such as a warrant or subpoena; others impose stricter consent-based controls. The rules in any particular jurisdiction may differ from the federal baseline, and the applicable framework depends on where the investigation was conducted and which agency ran it.

Fourth Amendment Questions

The central constitutional question is whether searching a genetic genealogy database counts as a “search” under the Fourth Amendment. If it does, law enforcement would generally need a warrant. If it does not, the searches can proceed under the terms set by the database platforms and agency policy.

The government’s strongest argument relies on the third-party doctrine, which holds that people surrender their expectation of privacy in information they voluntarily share with a company or service. Under that reasoning, uploading DNA to a public genealogy database carries the risk that the data might be accessed by others, including law enforcement. Lower courts have generally found that these searches do not violate the Fourth Amendment, though the case law is thin and no definitive ruling has reached the Supreme Court.

Defense attorneys push back on two fronts. The first invokes the Supreme Court’s 2018 decision in Carpenter v. United States, which held that accessing seven days of historical cell-site location data constituted a search requiring a warrant even though a third-party phone company held the records. The reasoning was that some digital records are so comprehensive and revealing that they deserve Fourth Amendment protection regardless of who stores them. Genetic data, which exposes family relationships, health predispositions, and ancestry, arguably fits that description even better than cell-tower records.

The second challenge targets abandoned DNA collection. The Supreme Court ruled in 1978 that trash left out for pickup carries no expectation of privacy, and most courts have extended that reasoning to discarded cups and cigarette butts. Several state courts have reached the opposite conclusion about trash searches, and critics argue that the deeply personal nature of DNA should require a warrant even when the physical sample was voluntarily discarded. Courts have not yet resolved whether Carpenter‘s logic extends to genetic material, and this remains the most likely path for a future challenge to reach the Supreme Court.

Uses Beyond Catching Suspects

The same methodology that identifies cold-case offenders also works for two other categories. The first is identifying unidentified human remains, sometimes called “John Doe” or “Jane Doe” cases, where a body or skeletal remains have never been connected to a known missing person. Both GEDmatch and FamilyTreeDNA permit law enforcement searches for this purpose, and even users who opt out of violent-crime matching on GEDmatch remain searchable for unidentified remains cases.⁷

The second is post-conviction testing. National guidelines for forensic genetic genealogy programs list post-conviction testing as a valid use case and recommend that agencies track requests from defense attorneys and post-conviction advocates.¹¹ The technique has been used to exonerate at least two wrongfully convicted individuals so far, with additional cases under review. If crime scene DNA can be matched to a family tree that points to someone other than the person who was convicted, that evidence can support a post-conviction challenge.

1
United States Department of Justice. Interim Policy on Forensic Genetic Genealogical DNA Analysis and Searching
2
PubMed Central. Forensic Genealogy, Bioethics and the Golden State Killer Case
3
Federal Bureau of Investigation. CODIS and NDIS Fact Sheet
4
PubMed Central. Bridging Disciplines to Form a New One: The Emergence of Forensic Genetic Genealogy
5
National Institute of Justice. Evaluation of Nuclear DNA from Rootless Hair for Forensic Purposes
6
PubMed Central. Four Misconceptions About Investigative Genetic Genealogy
7
GEDmatch. Terms of Service
8
FamilyTreeDNA. Law Enforcement Guide
9
23andMe. Transparency Report
10
Congress.gov. Advances in DNA Analysis: Fourth Amendment Implications
11
PubMed Central. National Technology Validation and Implementation Collaborative (NTVIC): Guidelines for Establishing Forensic Investigative Genetic Genealogy (FIGG) Programs