Imagine you voluntarily submit a DNA sample to learn more about your family history.
You are not suspected of a crime.
You have never been arrested.
You have never provided DNA to police.
But years later, investigators trying to identify an unknown suspect discover genetic information from a distant relative.
That relative might be you.
The investigators are not necessarily looking for the person who submitted the DNA. They may be looking for someone biologically related to that person.
That possibility has transformed criminal investigations.
For decades, forensic DNA analysis largely revolved around a straightforward question: Does biological material recovered from a crime scene match the DNA of a known person?
Genetic genealogy introduced a different question:
If there is no direct match, can the DNA lead investigators to the suspect's family?
The answer can be yes.
And that means one person's genetic information can potentially reveal something about people who never submitted DNA at all.
DNA Is Different From Most Other Identifiers
A password belongs to you.
A phone number can be changed.
A credit card can be replaced.
DNA is different.
Much of your genetic information exists because it was inherited from your biological parents, who inherited theirs from previous generations.
That means relatives share portions of their DNA.
Close relatives generally share more.
More distant relatives share less.
This biological relationship makes genetic information useful for genealogy.
It also creates something unusual from a privacy standpoint.
Information about one person can reveal biological relationships involving someone else.
You may never have taken a consumer DNA test.
But your biological relatives may have.
That can matter when investigators are trying to identify an unknown person from DNA.
Traditional Police DNA Databases Work Differently
Law enforcement has used DNA databases for decades.
The FBI's Combined DNA Index System, commonly known as CODIS, allows participating laboratories to compare qualifying forensic DNA profiles with other profiles in the system.
Traditional forensic DNA analysis generally examines specific genetic markers useful for identification.
If biological evidence recovered from a crime scene matches a known profile in a law-enforcement database, investigators can receive a powerful lead.
But sometimes there is no match.
The person who left the DNA may never have been entered into the database.
Historically, that could leave investigators with extraordinarily useful biological evidence but no name to attach to it.
Forensic genetic genealogy created another route.
The Justice Department describes the technique as combining DNA analysis and searching with traditional genealogical research to generate investigative leads, including leads that can help identify unknown suspects and unidentified human remains.
Investigators Don't Necessarily Need a Direct Match
Suppose DNA from an unknown suspect is compared through an appropriate genetic-genealogy process.
There is no direct match identifying the suspect.
But there is a partial genetic relationship to someone else.
That person may be a cousin.
Or a more distant relative.
The match does not simply announce:
“Your relative committed the crime.”
Instead, it can provide investigators with a starting point.
Genealogists can examine family trees, public records and biological relationships.
They may identify ancestors shared by the unknown person and the genetic match.
Then they can work forward through descendants.
Age matters.
Sex may matter.
Geography matters.
Family relationships matter.
Eventually, investigators may narrow a very large family tree to a much smaller group of people who could plausibly have left the crime-scene DNA.
The genealogy does not necessarily prove which person committed the crime.
It generates a lead.
The Genealogy Is Usually the Beginning, Not the End
This distinction is essential.
Suppose genetic genealogy points investigators toward one particular man.
That does not necessarily mean the genealogical search itself will be the final evidence establishing that his DNA matches the crime-scene sample.
Investigators may conduct additional traditional police work.
Where did he live when the crime occurred?
Was he the appropriate age?
Did he have access to the location?
Do other facts connect him with the crime?
Investigators may then seek a direct DNA sample through lawful investigative means.
That sample can be compared with the original crime-scene evidence.
The genealogy helped investigators determine where to look.
The direct comparison can provide much stronger identification evidence.
A Relative Can Become the Bridge
This is what makes genetic genealogy fundamentally different from many traditional investigative techniques.
A relative who has done nothing wrong can become the bridge between an unknown DNA sample and the person investigators are trying to identify.
Imagine a simplified family.
Two sisters each have children.
Those children have children.
Decades later, one branch of the family submits DNA to a genealogy database.
Someone in another branch becomes the subject of an investigation.
The two people may barely know each other.
They may never have met.
But their DNA still contains evidence of a biological relationship.
That relationship can potentially help genealogists connect the unknown DNA to the larger family.
The Technique Changed Cold-Case Investigations
Forensic genetic genealogy became particularly significant in investigations where biological evidence had been preserved for years but traditional DNA searches produced no suspect.
A homicide can remain unsolved for decades.
Witnesses die.
Memories fade.
Investigators retire.
Paper records become old.
But properly preserved biological evidence does not forget who produced it.
Advances in DNA analysis can allow investigators to revisit evidence using techniques that did not exist when the crime occurred.
That has made genetic genealogy especially important in cold cases involving homicide, sexual assault and unidentified remains.
The Department of Justice formally adopted an interim policy governing its use of forensic genetic genealogical DNA analysis and searching in covered investigations, reflecting both the technique's investigative potential and the need for rules governing its use.
Genetic Genealogy Is Not the Same Thing as CODIS
The distinction between traditional forensic DNA databases and genetic genealogy is important.
CODIS was created for law-enforcement DNA comparisons and operates under statutory and regulatory rules.
Genetic genealogy can involve a different type of genetic analysis designed to identify biological relationships.
The Justice Department's forensic-genetic-genealogy policy explains that traditional forensic DNA typing historically examined a limited set of STR markers and that CODIS compares forensic profiles with profiles maintained in designated law-enforcement indices.
Genealogical searching is designed to do something different.
Instead of asking only whether two profiles directly match, it can help identify people who share portions of DNA because they are biologically related.
That difference is what makes a distant cousin potentially useful to an investigation.
The Database Matters
Not every DNA database operates under the same rules.
A law-enforcement database is not the same thing as a commercial genealogy service.
And commercial or genealogy-oriented services can have different policies regarding law-enforcement access and investigative use.
Those policies can change.
Some services may prohibit particular uses.
Some may permit certain law-enforcement searches subject to restrictions.
Some may allow users to make choices concerning participation.
That means the statement “police can search DNA websites” is too broad to be useful.
The correct answer depends on the database, its policies, applicable law and the method investigators use to obtain or compare information.
For someone considering a genetic service, those distinctions can be important because DNA information is unusually persistent.
You Cannot Change Your DNA After a Privacy Policy Changes
A password can be reset.
An email address can be abandoned.
A compromised credit-card number can be canceled.
Your inherited genetic characteristics are different.
Once genetic information has been generated, it describes something that cannot simply be replaced.
And because relatives share DNA, the decision is not entirely individual in its consequences.
A person who submits DNA is primarily providing information about himself or herself.
But some of that information necessarily says something about biological relatives as well.
That does not mean a person needs permission from an extended family before taking a DNA test.
It does mean genetic privacy has a family dimension that ordinary account privacy does not.
Police Have Long Collected DNA in Other Contexts
The constitutional questions surrounding DNA did not begin with consumer genealogy.
In Maryland v. King, the Supreme Court considered a Maryland law allowing DNA collection through a cheek swab from certain people arrested for serious offenses.
Alonzo King was arrested in 2009 on assault charges. During booking, authorities took a cheek swab under Maryland's DNA law. The resulting profile matched DNA from an unsolved 2003 rape.
King challenged the DNA collection under the Fourth Amendment.
In 2013, the Supreme Court held that when officers make a probable-cause-supported arrest for a serious offense and bring the person to the station for detention, the cheek-swab DNA collection at issue was a reasonable booking procedure under the Fourth Amendment.
The decision was divided, with four Justices dissenting.
But Maryland v. King concerned government collection of DNA from an arrestee under a state statute.
Genetic genealogy raises different questions because the information may originate with people who voluntarily submitted DNA for non-law-enforcement purposes.
A DNA Match Is Powerful, but It Still Has to Be Interpreted Correctly
DNA evidence has an aura of certainty.
In some contexts, a properly obtained and analyzed direct DNA comparison can provide extraordinarily strong identification evidence.
But DNA does not answer every question in a criminal case.
Suppose a person's DNA is found inside a house.
That may strongly establish that biological material from that person was present.
It does not necessarily establish when it arrived.
It does not automatically establish why the person was there.
It does not by itself prove every element of a crime.
The surrounding circumstances still matter.
The same caution applies even more strongly to genealogical leads.
A relative's DNA does not prove another relative committed a crime.
It establishes a biological relationship that may help investigators identify candidates for further investigation.
Family Trees Can Contain Mistakes
Genealogy also involves ordinary human complications.
Official records can contain errors.
Names can change.
People can be adopted.
Parentage reflected in family records may differ from biological parentage.
Families can contain relationships unknown to later generations.
Two people with similar names can be confused.
A genealogical conclusion therefore requires careful research.
DNA can reveal a biological relationship, but converting that relationship into a correct family tree can involve records created over generations.
The farther investigators travel through a family tree, the more important careful verification becomes.
Investigators Can Narrow a Family Without Accusing Everyone in It
Imagine genealogy identifies a pair of great-great-grandparents shared by the unknown DNA source and a database user.
Those ancestors might have hundreds of living descendants.
Investigators can narrow the field using ordinary facts.
The unknown DNA may indicate biological sex.
The crime may have occurred in California.
Witnesses may have estimated an age.
The perpetrator may have attended a particular school, worked in a particular profession or owned a particular vehicle.
Public records may show which descendants lived in the relevant area at the relevant time.
The goal is not necessarily to investigate every relative as a suspect.
The genealogy provides structure that can help investigators determine which branches of a family tree are relevant.
A Person Can Help Identify a Relative Without Knowing It
This is perhaps the most surprising aspect of the technology.
Imagine someone takes a DNA test because she wants to identify her great-grandparents.
She never speaks with police.
She never knows about an investigation.
She has never met the distant cousin investigators ultimately identify.
Yet their shared ancestry can potentially provide a route through the family tree.
Nothing comparable happens when someone provides a fingerprint.
Your fingerprint does not reveal your cousin's fingerprint.
DNA is different because heredity connects people.
That is why the privacy debate extends beyond the individual who submits the sample.
The Same Technology Can Give a Name to the Dead
Forensic genetic genealogy is not used only to identify suspected perpetrators.
It can also help identify unknown human remains.
A body may be discovered without identification.
Traditional fingerprints may not produce a result.
Dental records may be unavailable.
A standard DNA database search may fail.
Genealogical analysis can potentially connect the unknown person's DNA with biological relatives and allow researchers to reconstruct the family.
The Justice Department specifically recognizes identification of unidentified human remains as one use of forensic genetic genealogy.
In those cases, the same technology that raises privacy questions can restore a name to someone who might otherwise remain unidentified.
The Legal Questions Are Larger Than a Single Investigation
Genetic genealogy forces several long-term questions into the same conversation.
How should law enforcement use genetic information originally provided for another purpose?
What restrictions should databases place on investigative searching?
How should users be informed about possible uses of their genetic information?
When should investigators be permitted to use genealogy?
How should leads be verified?
How should information about innocent relatives be handled?
What happens when technology becomes capable of drawing new conclusions from genetic information collected years earlier?
Those questions will continue even as individual companies, databases and policies change.
DNA Makes Privacy a Family Matter
Most privacy decisions seem personal.
You decide whether to share your location.
You decide whether to post a photograph.
You decide whether to publish your telephone number.
Genetic information does not fit neatly into that model.
Your DNA is uniquely yours, but much of its significance comes from the fact that portions of it are shared with biological relatives.
That is what makes genealogy possible.
It is also what makes forensic genetic genealogy possible.
A person may never provide DNA to police.
A person may never submit a sample to a consumer genetics company.
A person may never consent to having his or her genetic information searched.
Yet relatives can still create genetic clues pointing toward the family.
That does not mean a relative's DNA automatically identifies someone as a criminal.
It means investigators may acquire something they did not have before:
a path into the family tree.
And once investigators know which family to examine, traditional records, ordinary police work and ultimately direct DNA testing can sometimes take them the rest of the way.
That is why one of the most consequential facts about modern DNA evidence is also one of the simplest:
Your DNA does not describe only you.