Familial DNA Searches Using Public Databases and the Third-Party Doctrine

by Evan Enzer (J.D. 2021)

This blog was inspired by an episode of Slate’s podcast “If Then” entitled When Your DNA is Public Information. The podcast is available at https://slate.com/podcasts/if-then/2019/08/ancestry-and-genealogy-websites-crack-cold-cases-but-raise-privacy-concerns.

I. Introduction

Police departments have recently started using consumer DNA databases to conduct familial DNA searches, a practice that raises constitutional issues under the Fourth Amendment.[1] Prior to 2018, it seemed exceedingly likely that the Supreme Court would apply the third-party exception to a familial search,[2] but as will be discussed in Section III, the Supreme Court recently narrowed the application of this doctrine.[3] An added nuance is that familial DNA searches reveal information about people who did not volunteer their DNA.[4] Nila Bala, a criminal justice policy scholar, calls this a “fourth-party” consent issue.[5] The narrowing of the third-party doctrine and the issue of fourth-party consent brings the legality of familial searches into question.

II. Background

A familial DNA search uses genetic material collected from crime scenes to match and locate similar samples in a DNA database.[6] Investigators compare collected genetic information to material in the database to identify potential suspects by locating their family members.[7] Once a match is found, police officers then collect a DNA sample from the suspect and compare it to the DNA collected at the crime scene.[8]

Although familial DNA searches are not new,[9] the scope of their use has been expanded in recent years.[10] In Maryland v. King, the Supreme Court upheld a state statute that allowed law enforcement to collect DNA from individuals arrested for violent crimes.[11] Today, every state collects DNA samples from individuals convicted of felonies.[12] King did not address whether these government databases can be used for familial searches, but nearly every state allows the practice.[13] Police have now expanded the scope of their search by using public databases in addition to government databases.[14]

III. Third Party Doctrine

The third-party doctrine is an exception to the Fourth Amendment’s warrant requirement.[15] The doctrine allows the government to obtain information that a person voluntarily shared with a third party.[16] This doctrine was recently limited by the U.S. Supreme Court in Carpenter, when it found that the exception does not apply to cell phone location data because it reveals extensive personal information.[17] Carpenter acknowledged that  while there is a limit to the third-party doctrine, the doctrine is still good law.[18]

It is not clear whether the third-party doctrine applies to sharing genetic information with public DNA databases.[19] The DNA in question was voluntarily shared with the database, suggesting that the third-party doctrine applies. However, a DNA sample can potentially reveal more personal information than cell phone location data.[20] This suggests that the limit imposed by Carpenter may apply to searching a DNA database. Additionally, familial searches are not meant to reveal information about the individual who volunteered the DNA. Rather, they are designed to identify one of the volunteer’s family members.[21] Therefore, familial DNA searches fall outside the usual scope of the third-party doctrine.

Two lower state court cases suggest that using public databases for familial DNA searches is constitutional.[22] In the trial of William Talbott II, the parties agreed to treat familial searches akin to a traditional tip, and the judge did not rule on the issue.[23] In the trial of Jesse Bjerke, the court held that familial searches ”did not reveal private, personal information other than [the suspect’s] identity . . . .”[24] While these cases do not settle the constitutional question, they are early signs that courts will find that using a public database for a familial search does not violate the Fourth Amendment.

IV. Conclusion

Familial searches using public databases are becoming a high-profile topic, and it would not be surprising for the Supreme Court to address their constitutionality soon. Trial court have found familial DNA searches constitutional, but the law is still unsettled. While this suggests that the third-party doctrine applies to public DNA databases, Carpenter shows that the Court is willing to limit the doctrine. Therefore, the Court might limit the government’s ability to use public DNA databases for familial searches, and ambitious attorneys should consider challenging familial DNA searches under the Fourth Amendment.


[1] See Megan Molteni, The Key to Cracking Cold Cases Might Be Genealogy Sites, Wired (June 1, 2018, 7:00 AM), https://www.wired.com/story/police-will-crack-a-lot-more-cold-cases-with-dna [https://perma.cc/Y88H-EN5K]; Erin Murphy, Relative Doubt: Familial Searches of DNA Databases, 109 Mich. L. Rev. 291, 334–35 (2010).

[2] See When Your DNA is Public Information, Slate (Aug. 21, 2018), https://slate.com/podcasts/if-then/2019/08/ancestry-and-genealogy-websites-crack-cold-cases-but-raise-privacy-concerns [https://perma.cc/TLH8-3JGT].

[3] Carpenter v. United States, 138 S. Ct. 2206, 2216–17 (2018).

[4] See Lars Trautman & Nila Bala, Golden State Killer Case Ushers in New Era of Fourth Party Consent, The Brookings Institution (July 3, 2018), https://www.brookings.edu/blog/techtank/2018/07/03/golden-state-killer-case-ushers-in-new-era-of-fourth-party-consent [https://perma.cc/3XXZ-QWGK].

[5] Id.

[6] See Murphy, supra note 1, at 297–98.

[7] See id. at 298.

[8] See id.

[9] See id. at 292.

[10] Police have only started using public databases within the last few years. See Molenti, supra note 1.

[11] See 569 U.S. 435, 465–66 (2013).

[12] See Elizabeth E. Joh, Should Arrestee Databases Extend to Misdemeanors?, 8 Recent Advances in DNA & Gene Sequences 59, 61 (2014).

[13] 569 U.S. at 444; see Trautman & Bala, supra note 4.

[14] See Molenti, supra note 1.

[15] See Carpenter v. United States, 138 S. Ct. 2206, 2216 (2018).

[16] See id.

[17] See id. at 2216–17.

[18] See id. at 2216.

[19] See When Your DNA is Public Information, supra note 2.

[20] See Murphy, supra note 1, at 315–16; but see Maryland v. King, 569 U.S. 435, 445 (2013).

[21] See Trautman & Bala, supra note 4.

[22] See Rachel Weiner, Alexandria Rape Case Based on Database Search to go Forward, Washington Post (July 11, 2019, 3:49 PM), https://www.washingtonpost.com/local/public-safety/alexandria-rape-case-based-on-dna-database-search-to-go-forward/2019/07/11/782eaa8a-a417-11e9-bd56-eac6bb02d01d_story.html [https://perma.cc/R84S-EBLY].

[23] See Megan Molenti,  A Murder Trial Will Allow DNA Evidence From a Geneaology Site, Wired (June 11, 2019, 3:31 PM), https://www.wired.com/story/a-murder-trial-will-allow-dna-evidence-from-a-genealogy-site/ [https://perma.cc/N67V-BBW4].

[24] See Weiner, supra note 22.