Do Criminal Suspects Have Reasonable Expectations of Privacy to Their Family Members’ DNA?

Photo by Louis Reed on Unsplash

Baylee Kalmbach, Associate Member, University of Cincinnati Law Review

I. Introduction

“No two people have the same DNA, meaning the use of such evidence can either prove a person’s innocence or guilt with great accuracy.”[1] True, while no one has identical DNA to another, individuals still “share around 50% of [their] DNA with parents and children, 25% with grandparents and grandchildren, and 12.5% with cousins, uncles, aunts, nephews, and nieces.”[2] Beyond identifying members of a family, DNA evidence can be used to identify criminal suspects with a high degree of certainty.[3] More recently, criminal defense and post-conviction attorneys have used DNA evidence retroactively to prove that law enforcement may have convicted the wrong criminal suspect.[4] Unlike other types of evidence used against criminal defendants, absent any contamination, “crime framing,” or other ethical issues, DNA evidence is the type of science the criminal legal system can rely on.[5]

While the use of DNA obtained from a crime scene to identify a criminal suspect is supported by both proponents and critics of the criminal legal system,[6] the use of a criminal suspect’s family member’s DNA obtained from a third-party database is much more criticized.[7]  The following sections will provide background on Fourth Amendment jurisprudence, DNA evidence, as well as genetic genealogy and how it has been used in the last four years to identify criminal suspects. It will discuss whether people should have reasonable expectations of privacy to their family members’ DNA, and whether this type of intrusion is one where investigators must first receive a warrant supported by probable cause.

II. Background

Criminal suspects have constitutional rights under the Fourth Amendment to the United States Constitution, which addresses the extent that their bodies and property can be searched or seized.[8] This section will discuss the intersection of this constitutional protection with DNA evidence and genetic genealogy.

A. DNA Evidence

Sir Alec Jeffreys revolutionized criminal investigations in 1984 when he discovered DNA testing could be used to identify individuals suspected of crimes.[9] The first case DNA was used to successfully identify and convict a wanted criminal suspect. Police had a suspect who confessed to the murder.[10] Yet, his genetic code did not match the profile left at the crime scene.[11] Instead, for the first time, DNA was used to compare more than 4,000 men’s blood and saliva samples to eventually come up with a match, successfully identify who left their DNA behind, and ultimately find who was responsible for the murder.[12]

Since 1984, DNA profiling, extraction, and differentiation techniques have significantly improved and advanced.[13] For example, forensic scientists can now target male DNA with the use of Y-STR testing (Y-chromosomal testing),[14] determine the number of profiles in a mixed DNA sample,[15] and even extract DNA off spent bullet shell casings.[16] While other types of forensic science like fingerprinting, hair analysis, and bite mark evidence can be unreliable bases for criminal convictions, “DNA profiling has become the gold standard in forensic science.”[17] Besides simply using it to bolster other evidence, ensure police got the right guy, and ultimately convict him, DNA can also be used to point to an unidentified suspect where no other evidence exists.

B. Genetic Genealogy  

“Genetic Genealogy (GG) is the combination of genetic analysis with traditional historical and genealogical research to study family history.”[18] It can be used to identify biological relationships among groups of people, create family trees, and solve mysteries in immediate families like identifying parents of adopted children or babies swapped at birth.[19] 

The public’s use of the global genealogy and ancestry industry has rapidly increased over the last few years and will likely continue to grow at a remarkable rate.[20] Websites like, FamilySearch, Findmypast, and MyHeritage all offer similar paid services in documenting family relations and identifying ancestors across the globe.[21] Unlike these four leading ancestry-tracking companies, other databases like are free and fully accessible for public use, including by law enforcement.[22]

For instance, after evading the government for decades, in 2018, Joseph DeAngelo, widely known as the “Golden State Killer,” was finally captured when investigators for the first time used and discovered nearly 20 of DeAngelo’s relatives voluntarily uploaded their DNA to it.[23] Since then, genetic genealogy has been used to identify more than 80 criminal suspects with the use of their family members’ DNA.[24]

Today, hosts over 1.4 million DNA profiles from across the globe.[25] With widespread law enforcement access and use of it, along with other public databases or third-party ancestry websites, an individual’s at home DNA test kit can be used to identify her relative who is suspected of a crime.[26]

C. The Fourth Amendment

The Fourth Amendment protects people from warrantless searches or seizures.[27] Its most significant purpose “is to safeguard the privacy and security of individuals against arbitrary invasions by governmental officials.”[28] Instead of providing blanket-protections against unreasonable intrusions, Fourth Amendment jurisprudence offers constitutional protection only where individuals have reasonable expectations of privacy, and where the government has unlawfully intruded that space and expectation.[29]  First articulated in Justice Harlan’s concurrence in Katz v. United States, the “reasonable expectation of privacy test” seeks to first determine whether the individual can claim “a legitimate expectation of privacy” by asking whether (1) an individual has exhibited an actual (subjective) expectation of privacy; and (2) the expectation is one that society is prepared to recognize as reasonable.[30]

“The Court has twice held that individuals have no Fourth Amendment interests in business records which are possessed, owned, and controlled by a third party.”[31] However, in Carpenter v. United States, the Supreme Court in 2018 held that “an individual’s reasonable expectation of privacy under the Fourth Amendment is not eliminated simply because records are held by a third party.”[32] The Carpenter Court emphasized that the “third-party doctrine”—a doctrine holding that individuals have no reasonable expectations of privacy in information held by third parties—considers the level of intrusion by the government and applies where individuals have voluntarily exposed the information to a third party with affirmative acts.[33] In sum, Carpenter clarified that there is no bright-line rule to expectations of privacy when it comes to information held by third parties, but also emphasized it will be a “rare case where the suspect has a legitimate privacy interest” in this type of information.[34]

The Court has yet to address the question of whether DNA held by a third party is the type of “rare case” where a criminal suspect has Fourth Amendment protections.

III. Discussion

Criminal suspects certainly do not have a reasonable expectation of privacy to their own DNA that they left in the commission of a crime.[35] The question remains: Do criminal suspects have a reasonable expectation of privacy in the government’s use of their family’s DNA? This section will discuss how genetic genealogy implicates new issues within Fourth Amendment protection and jurisprudence, as well as nuances with expectations of privacy, DNA, and the third-party doctrine.

A. Third-Party Doctrine and DNA Databases

As the Carpenter Court recently concluded, simply because information is held with a third party does not strip an individual’s Fourth Amendment protections. Yet, it does not necessarily follow that the Fourth Amendment prohibits police from using third-party public databases to identify criminal suspects who left their DNA behind in the commission of a crime.   

At issue in Carpenter was if an individual can claim a reasonable expectation of privacy in her cell-site location information (“CSLI”) spanning over 127 days, when that information was held by third-party cell-phone providers.[36] By emphasizing the “intimate window into a person’s life” that is revealed by CSLI, including “familial, political, professional, religious, and sexual associations,” the Court held that CSLI revealed too much information for police to access without first having a warrant supported by probable cause.[37]

Similarly, DNA can reveal an abundance of intimate information, such as familial associations, ancestry, ethnicity, but also potential genetic variations that an individual could be at risk for certain diseases like Alzheimer’s or cancer.[38] Because of the amount of private information it could reveal, if a court were presented with the issue of familial DNA obtained from a third-party database, this emphasis in Carpenter would likely tip the scale toward requiring police to obtain a warrant in order to upload a criminal suspect’s DNA to a public database and search for relatives.

In United States v. Smith, the Court held that “a person has no legitimate expectation of privacy in information he voluntarily turns over to third parties.”[39] It previously clarified that this is true “even if the information is revealed on the assumption that it will be used only for a limited purpose,” in United States v. Miller.[40] Without Carpenter, the result of familial DNA searches would be relatively clear, then: law enforcement can obtain information from a third-party database without violating the constitutional protections of criminal suspects, and without a warrant, because criminal suspects do not have expectations of privacy in information held by third parties.

However, also at issue in Carpenter was whether the third-party doctrine even applies if individuals invoking Fourth Amendment protection did not provide the information to the third-party affirmatively or voluntarily.[41] Carpenter clarified that while cellphone users “voluntarily” send data when they use them to communicate, users do not “voluntarily” log their records with affirmative acts, and there is “no way to avoid leaving behind a trail of location data.”[42]

Under the Smith Court’s voluntariness requirement, and the Carpenter Court’s articulation of it, while criminal suspects affirmatively leave their DNA behind in the commission of a crime, they certainly do not voluntarily submit their family members’ DNA to a third-party database for comparison to their own. Therefore, while familial DNA searches seem to be outside of the scope of the third-party doctrine and would likely result in suspects not automatically losing their Fourth Amendment protections just because the information is on a third-party database, the question remains if criminal suspects can claim a reasonable expectation of privacy in another’s DNA in the first place.

B. Are Expectations of Privacy in Another’s DNA Reasonable?

As the Supreme Court held in Alderman v. United States, “Fourth Amendment rights are personal rights which, like some other constitutional rights, may not be vicariously asserted.”[43] As follows, it would be extremely difficult to reason that criminal suspects have reasonable expectations of privacy in another’s DNA. Further, the Court has said that “[l]egitimation of expectations of privacy by law must have a source outside of the Fourth Amendment,” like property interests in the home.[44] Similarly, as mentioned above, criminal suspects certainly do not have reasonable expectations of privacy in their own DNA that they leave behind while committing a crime,[45] because “[w]hat a person knowingly exposes to the public…is not a subject of Fourth Amendment Protection.”[46]

Even assuming the court could conclude criminal suspects should have privacy interests in their family members’ DNA, it would also be difficult to determine whether society is willing to accept a privacy expectation of another’s DNA as “reasonable,” which is the second requirement in Justice Harlan’s test.[47] Because the use of DNA and genetic genealogy as a crime-solving tool is relatively new, it is difficult to predict what society believes about this practice “before its role in society has become clear.”[48]

IV. Conclusion

While some view the use of genetic genealogy to locate criminal suspects as revolutionary and implicating “nothing new, legally or ethically,”[49] others say DNA databases are a “menace to privacy” and muddy the waters within Fourth Amendment protections.[50] With seemingly little constitutional protections to avoid the use of DNA databases by law enforcement (so far), users voluntarily uploading their DNA to these public websites should do so with caution and understanding that their DNA can be used for far more than mapping out a family tree.

[1] Jarrett P. Ambeau, Pros and Cons of DNA Evidence, Ambeau Law (Jul. 21, 2020),,or%20guilt%20with%20great%20accuracy.

[2] Daniella Levy, What Is a Good DNA Match from a Research Perspective, MyHeritage (Fed. 19, 2020),,aunts%2C%20nephews%2C%20and%20nieces.&text=A%20match%20of%203%25%20or,research%20%E2%80%94%20but%20sometimes%20even%20less.

[3] See Ambeau, supra note 1.

[4] Id.

[5] Using DNA to Solve Crimes, The U.S. Department of Justice Archives (Mar. 7, 2017),,accused%20or%20convicted%20of%20crimes. See also Overturning Wrongful Convictions Involving Misapplied Forensics, Innocence Project,

[6] How DNA Evidence Works, FindLaw (Feb. 8, 2019),

[7] Lindsay Van Ness, DNA Databases Are Boon to Police But Menace to Privacy, Critics Say, PEW Trusts (Feb. 20, 2020),

[8] U.S. Const. amend. IV.

[9] Celia Henry Arnaud, Thirty years of DNA forensics: How DNA has revolutionized criminal investigations, c&en (Sept. 18, 2017),

[10] Id.

[11] Id.  

[12] Id.  

[13] Id.

[14] Y-STR Testing: Enhancing Sexual Assault and Cold Case Workflows, SAKITTA, (last visited Apr. 29, 2022).

[15] Rich Press, DNA Mixtures: A Forensic Science Explainer, NIST (Apr. 3, 2019),

[16] Seth Augenstein, DNA off Spent Shell Casings a Matter of Getting in the Nooks and Crannies, Forensic Mag (Aug. 24, 2018),

[17] See Arnaud, supra note 9.

[18] Snapshot Genetic Genealogy, Parabon Nanolabs,,likely%20identity%20of%20a%20perpetrator (last visited Apr. 14, 2022).

[19] Id.

[20] Genealogy Products and Services Market Trends Analysis, DATAINTELO, (last visited Apr. 14, 2021).

[21] Sunny Jane Morton, Genealogy Websites Comparison:, FamilySearch, Findmypast and MyHeritage, familytree, (last visited Apr. 14, 2022).

[22] Tomohiro Takano, How to Use GEDMATCH – Is It Safe? | Beginner’s Guide, Genomelink Blog (Sept. 20, 2021),

[23] JV Chamary, How Genetic Genealogy Helped Catch The Golden State Killer, Forbes (June 30, 2020),

[24] See Van Ness, supra note 7.

[25] GEDmatch, (last visited Apr. 29, 2022).  

[26] Carolyn Y. Johnson, Even if you’ve never taken a DNA test, a distant relative’s could reveal your identity, The Washington Post (Oct. 11, 2018),

[27] U.S. Const. amend. IV.

[28] Camara v. Mun. Court of City and Cty. Of San Francisco, 387 U.S. 523, 528 (1967).

[29] Katz v. U.S., 389 U.S. 347, 354 (1967).

[30] Id. at 361.

[31] Carpenter v. U.S., 138 S.Ct. 2206, 2223 (2018); United States v. Miller, 425 U.S. 435 (1976); Smith v. Maryland, 442 U.S. 735 (1979).

[32] Ohio v. Eads, 154 N.E.3d 538, 546 (2020); Carpenter v. United States, 138 S. Ct. 2206, 2217 (2018).

[33] Carpenter, 138 S. Ct. at 2210.

[34] Id. at 2211.

[35] Charles Stimson & Zack Smith, GEDMatch and the Fourth Amendment: No Warrant Required, The Heritage Foundation (May 13, 2021),

[36] Carpenter, 138 S. Ct. at 2212.  

[37] Id. at 2219.

[38] Sonya Collins, What Secrets Can Genetic Tests Really Reveal?, WebMD (Dec. 27, 2018),

[39] Smith v. Maryland, 442 U.S. 735, 741 (1979).

[40] United States v. Miller, 425 U.S. 435, 443 (1976).

[41] Carpenter v. U.S., 138 S. Ct. 2206, 2219 (2018).

[42] Id. at 2220.

[43] Alderman v. U.S., 394 U.S. 165, 174 (1968).  

[44] Katz v. U.S., 389 U.S. 347, 354 (1967).

[45] See Stimson & Smith, supra note 35.

[46] Katz, 389 U.S. at 351.

[47] Id. at 361.  

[48] Ontario v. Quon, 560 U.S. 746, 759 (2010).

[49] Teneille R. Brown, Why We Fear Genetic Informants: Using Genetic Genealogy to Catch Serial Killers, 21 Colum. Sci. & Tech. L. Rev. 118, 118 (2019).

[50] See Van Ness, supra note 7.


  • Baylee grew up in Erie, MI on the Lost Peninsula. She is an avid boater, dog mom, and Oakland Raiders fan. Passionate about disability rights and employment law, she chose to write her Comment on COVID-19's impact on the right to telework as a reasonable accommodation under the ADA. For her various blog posts, she wrote about taxing requirements for third-party payment applications, medical rationing during the pandemic, racism in the NFL, and genetic genealogy's impact on criminal suspects' constitutional rights. She hopes to become a litigator and educate people on forward-thinking business and employment practices. Read Baylee's published Student Comment, A COVID Silver Lining? How Telework May Be a Reasonable Accommodation After All, at the hyperlink below.

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