Saturday, June 23, 2018

Trawling Genealogy Databases and the Fourth Amendment: Part I

Law-enforcement use of a DNA database created for genealogy enthusiasts helped discover the man believed to be the Golden State Killer. It also provoked an immediate outpouring of media reports of concerns about "genetic privacy." Now, essays from groups of bioethicists and lawyers have appeared in both the Annals of Internal Medicine [1] and Science [2]. Neither article gives a convincing and complete analysis of the legal issues—hardly surprising given the word limits for such policy forum essays—but both are useful as starting points for discussion.

I. The Misplaced “Abandonment” Theory

The Annals article, Is It Ethical to Use Genealogy Data to Solve Crimes? [1], assures us that the law provides “clarity.” The authors find this clarity in “the abandonment doctrine.” The following paragraph comprises their entire legal analysis:
The legal questions raised by genealogy searches are measurably simpler than the ethical concerns. In terms of the U.S. Constitution, a genealogy search triggered by DNA collected from a crime scene probably would not count as a “search” under the Fourth Amendment (4). Even assuming it would, the applicable legal theory—the “abandonment doctrine”—holds that a person has no “reasonable expectation of privacy” in abandoned materials. Courts have allowed law enforcement to test DNA “abandoned” in a range of settings (such as hair clippings and discarded cigarette butts). At genealogy Web sites, users voluntarily upload (that is, abandon) familial data into commercial databases. Whether they are aware that their data are subject to police collection is, legally, irrelevant (5). Notwithstanding the clarity of the law, it is questionable whether it is good social policy to consider the uploading of genealogic data the same as abandoning DNA in a public space.
These remarks confuse two very different questions. The first is whether a data-gathering method is a search within the meaning of the Fourth Amendment. The Amendment protects against “unreasonable searches and seizures” of “persons, houses, papers, and effects,” in large part by requiring police to acquire judicial warrants based on probable cause before undertaking a search or seizure. (Reliance on a properly issued warrant makes the search reasonable.)

But not all information collection is a search or seizure that triggers the Fourth Amendment demand for reasonableness. For example, a police officer who merely watches a shady character—or anyone else—walk down the street has not searched or seized anyone. If the officer snaps a photo of the person and compares it to photos of wanted criminals, there is still no search or seizure, for there has been no interference with the individual’s body, movements, or property. And if no search has occurred, there is no need to ask whether the officer’s decision to study the individual was reasonable in light of the facts known to the officer. The notion that what a person knowingly exposes to the general public cannot be the subject of a “search” is sometimes called the “public exposure doctrine.” It pertains to the threshold question of whether a search has occurred.

The “abandonment doctrine” also applies to this threshold question. It applies to property that a person has discarded or left behind. If the police see an individual throw away a syringe, they may collect it and then analyze it for the presence of heroin without obtaining a warrant—because they have not performed a search that affects any legitimate interest. By intentionally relinquishing the syringe, the individual has given up any property interest. He or she might not want it to become known that the syringe has traces of heroin in it, but if heroin possession is a criminal act, then the individual can hardly claim that the interest in keeping this fact secret is legitimate and hence protected by the Fourth Amendment. So the abandonment doctrine is another route to a conclusion that the police have conducted no search or seizure within the meaning of the Amendment.

The lower courts have almost always applied the abandonment doctrine to DNA molecules shed or deposited in both legal and illegal activities. But it is odd to maintain, as Is It Ethical? does, that abandonment makes a search reasonable because “a person has no ‘reasonable expectation of privacy’ in abandoned materials.” That mistakes the question of whether a search is justified for the question of whether the police conduct is a search. The “reasonable expectation” standard, introduced in Katz v. United States, 389 U.S. 347 (1967), is merely a way to show that police have engaged in a search; it is not a way to show that a search is reasonable.

This distinction may sound finicky. Functionally, what is the difference between (1) defining everything as a search, but then asking whether the investigation is reasonable because there is no reasonable expectation of privacy in the items searched, and (2) asking whether there is a search because there is no reasonable expectation of privacy in the first place? Nevertheless, no court that is faithful to the Supreme Court's many Fourth Amendment opinions would adopt the position contemplated in Is It Ethical?. No such court would write that even though profiling DNA from a crime-scene is a search, it does not require a warrant (or an exception to the generally applicable warrant requirement for a search to be constitutionally reasonable).

More importantly, the opinions allowing the police to profile shed DNA and compare the identifying profile with a suspect's DNA (or with all the profiles in a law enforcement DNA database), all without a warrant, do not demonstrate that police can also trawl a database of DNA sequences to see who might be related to whom. Further analysis is required to determine the constitutionality of familial, or other-directed searching by the state in both law-enforcement [3] and private (i.e., non-governmental) databases such as GEDmatch and the more restrictive commercial ones.

With respect to the private databases, the state's argument lies not so much in abandonment as in public exposure. The very reason the individual puts DNA data on the database is to enable curious members of the public to inspect it. As such, the Fourth Amendment issue is whether police (without a warrant) can do what anyone else can—namely, trawl the database for a partial match indicative of a genetic relationship to the suspect whose DNA is associated with a crime. In many contexts—overflying private property to get a look at what is there, for example—the Supreme Court has reasoned that what is open to the public generally is open to the police as well. Indeed, the Court has even held that entrusting or conveying information to private parties defeats the claim of a reasonable expectation of privacy and hence the claim of a search that requires probable cause and a warrant. Exposure to a small slice of the public—even a banker or a telephone company—is enough let the police in without a showing of probable cause. (Disclosure of information to one’s lawyer may be protected by the attorney-client privilege but not the Fourth Amendment.)

In the past several years, however, some Justices have evinced discomfort with this “third-party doctrine.” Just yesterday, the Court held in Carpenter v. United States, No. 16–402, 2018 WL 3073916 (U.S. June 22, 2018), that certain data generated by a cell-phone service provider—the third party—is not outside the protective umbrella of the Fourth Amendment just because it has been given to or generated by a third party. The data in the case amounted to extended tracking of the past whereabouts of a person’s cellphone’s via the electronic tracks, so to speak, left at cell towers. That information, the majority reasoned, was so sensitive as to make its possession by the cellular phone service providers insufficient to defeat the claim of a reasonable expectation of privacy. A warrant was required.

The Science article correctly frames the pivotal Fourth Amendment issue as the scope of the third-party doctrine, but it leaves much unsaid. I will turn to the implications of this evolving doctrine for trawls of genealogy databases in a later installment.


1. Benjamin E. Berkman, Wynter K. Miller & Christine Grady, Is It Ethical to Use Genealogy Data to Solve Crimes?, Annals Internal Med., May 29, 2018, DOI: 10.7326/M18-1348.
2. Natalie Ram, Christi J. Guerrini & Amy L. McGuire, Genealogy Databases and the Future of Criminal Investigation, 360 Science 1078-1079 (2018) DOI: 10.1126/science.aau1083
3. David H. Kaye, The Genealogy Detectives: A Constitutional Analysis of “Familial Searching”, 51 Am. Crim. L. Rev. 109 (2013),

Tuesday, June 5, 2018

DNA Evidence and the Warrant Affidavit in the Golden State Killer Case

Last Friday, Sacramento Superior Court Judge Michael Sweet “ordered arrest and search warrant information in the East Area Rapist/Golden State Killer case unsealed after weeks of arguments between attorneys over how the release would impact the trial of suspect Joseph James DeAngelo.” 1/ The 171 heavily redacted pages of documents did not discuss the kinship trawl of the publicly accessible genealogy database that occupied much of the news about the case. However, they did refer to later DNA tests of surreptiously procured samples of DeAngelo’s DNA:
     [I]nvestigators didn't have a sample of DeAngelo's DNA, so Sacramento sheriff's detectives began following him as he moved about town, finally watching April 18 as DeAngelo parked his car in a public parking lot at a Hobby Lobby store in Roseville, according to an arrest warrant affidavit unsealed Friday.
     "A swab was collected from the door handle while DeAngelo was inside the store," according to the affidavit from sheriff's Detective Sgt. Ken Clark. "This car door swab was submitted to the Sacramento DA crime lab for DNA testing." ... The swab contained DNA from three different people, and 47 percent of the DNA came from one person, the affidavit said.
     That DNA was compared to murders in Orange and Ventura counties where DNA had been collected and saved from decades before, and it came back with results that elated investigators. "The likelihood ratio for the three-person mixture can be expressed as at least 10 billion times more likely to obtain the DNA results if the contributor was the same as the Orange County/Ventura County (redacted) profile and two unknown and unrelated individuals than if three unknown and unrelated individuals were the contributors," Clark wrote in his affidavit seeking an arrest warrant for DeAngelo. ...
     Sacramento County District Attorney Anne Marie Schubert has said previously that even with the possible match she asked for a better sample, so investigators went hunting again, this time focusing on DeAngelo's trash on April 23.
     "The trash can was put out on the street in front of his house the night before," Clark wrote. "DeAngelo is the only male ever seen at the residence during the surveillance of his home which has occurred over the last three days."
     Detectives gathered "multiple samples" from the trash can and sent them to the crime lab on Broadway for analysis. "Only one item, a piece of tissue (item #234-#8), provided interpretable DNA results," Clark wrote."The likelihood ratio for this sample can be expressed as at least 47.5 Septillion times more likely to obtain the DNA results if the contributor was the same as the Orange County/Ventura County (redacted) profile than if an unknown and unrelated individual is the contributor." 2/
Compare this statement of the likelihood ratio to the misstated version from a “senior science writer” for Forensic Magazine:
The warrants now show that: ... [t]he additional surreptitious sample was from DeAngelo’s trash can set out at the curb. Only one piece of tissue provided interpretable DNA results, but those translated to a likelihood that DeAngelo was 47.5 septillion times more likely to be the Golden State Killer than an unknown and unrelated individual. 3/
To see the error, click on the label “transposition” in this blog. Of course, one can ask what’s the big deal when the likelihood ratio is in the septillions. But that question translates into an argument about harmless error. Sometimes the errors associated with sloppy phrasing won’t have immediate repercussions, but a magazine written for forensic practitioners ought not propagate sloppy thinking. In any case, things are looking up when detectives take the care to avoid transposing their conditional probabilities.

  1. Sam Stanton & Darrell Smith, Read the Warrant Documents in the East Area Rapist Case, Sacramento Bee, June 1, 2018,
  2. Sam Stanton & Darrell Smith, How Detectives Collected DNA Samples from the East Area Rapist Suspect, Sacramento Bee, June 1, 2018,
  3. Seth Augenstein, Golden State Killer Warrants Show Evolution of Killer — But Not Genealogy, Forensic Mag., June 4, 2018,