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Use of Forensic Genetic Genealogy Searches to Identify Suspects Needs Regulation and Can Be Challenged

by Matthew Clarke

Ever since it was used to identify the Golden Gate Killer in 2018, Forensic Genetic Genealogy (“FGG”) has been accepted by law enforcement as a tool for identifying unknown suspects. Most people view it as just another DNA profiling method, similar to that used to create the nationwide FBI-maintained CODIS database containing 21 million DNA profiles of people who have been arrested for or convicted of a crime. But, unlike a CODIS profile, which can do little more than determine whether a sample from a crime scene is similar to one in the database, an FGG profile can reveal a great deal of medical and familial information about a person. Thus, unlike CODIS, the use of FGG raises a number of privacy concerns that have not yet been ruled on by the highest courts, leaving FGG open to challenges by defense attorneys.

DNA is a molecule consisting of two strands of chemical building blocks called nucleotides connected together in a twisted double helix often depicted as a spiral ladder. The nucleotides are usually referred to by the first letter of their biochemical names, A, T, C, and G. They are strongly bonded along the length of the strand but only weakly bonded to the nucleotides in the other strand with the restriction that A can only bond to T and G can only bond to C. This arrangement allows the two strands to “unzip” for replication then close back up again.

The places where two nucleotides are weakly bonded, the “rungs” of the “ladder,” are called sites. Human DNA contains millions of sites, many of which are the same in everyone but some of which differ between individuals and are referred to as “polymorphic.” The polymorphic sites determine individual characteristics such as hair, skin, and eye color; hair texture; facial shape; blood type; and other factors that allow the immune system to identify cells as belonging to one’s self. It is the polymorphic sites that are the most useful for DNA testing. A CODIS profile consists of 20 sites while an FGG profile contains hundreds of thousands of sites.

There are two types of FGG databases. Sites like 23andMe and are closed sites that control and can limit search results and access to other users’ data. Notably, both require a search warrant before they will allow law enforcement access to their databases for FGG. Sites like GEDmatch, FamilyTreeDNA, and MyHeritage are open sites and permit a great deal of access to search other users’ data. They also have a history of allowing FGG searches, although some have recently required users to opt in to permit that use of their profiles.

DNA is typically measured in centimorgans (“cMs”) when it is used for genealogy. This is an assessment of the likelihood that a DNA segment will be passed on to a descendant intact. The closer the relationship, the longer segments are shared. Typically, you share 2,000 - 3,600 cMs with your parents, children, and siblings but only 425 - 1100 cMs with your first cousin.

A weakness of FGG is that it does not reveal familial relationships but rather degrees of relationship. That and the fact that recombination of inherited DNA is random means that someone you share 1,500 cMs with could be your grandparent/child, great grandparent/child, half-sibling, great uncle, or first cousin. Thus, the second phase of FGG starts after the DNA relationship is discovered, and it involves conventional genealogy, a search of documentation to discover ancestors.

A typical result is for a database to turn up three or more distant relations using DNA. Searches of records such as birth and death certificates, marriage licenses, obituaries, and even social media to “build [a family tree] backward” identify the most recent common ancestor those people had. Then they “build forward” to identify the person or group of persons most likely to have the suspect DNA. Law enforcement typically contracts this part of the investigation to a “genetic genealogist” or private company.

Then each suspected person is surveilled until an item containing their DNA – such as a disposable coffee cup, soda can, or straw – is publicly discarded. The item is then retrieved from the trash, and the DNA on it used to generate a profile that is compared to the profile of the DNA from the crime scene. This DNA comparison becomes the basis of the arrest, but defense attorneys are often not even told about the extensive FGG that led to police identifying the defendant.

GEDmatch is different from the other databases in that it does not create DNA profiles but rather allows users to upload profiles created by other companies. This gives users the ability to search through multiple companies’ databases to the extent they have been uploaded to GEDmatch.

By 2020, GEDmatch had 1.45 million users or 0.5% of the U.S. population. A user base of 2% is enough to identify 90% of the population, and given the rapid growth in GEDmatch users, this will happen within a few years. A 2022 agreement between GEDmatch and Family TreeDNA already allows law enforcement to identify 90-95% to third cousin or closer and 60% to second cousin.

Unlike the highly-regulated use of government-run DNA databases, there is little regulation of FGG using private databases. The U.S. Department of Justice has rules limiting the use of FGG to violent crimes and prohibiting FGG results as being the sole basis for an arrest, but the rules have not been formalized.

Only two states regulate FGG. Montana requires a warrant to be issued before performing any kind of DNA database search. Maryland’s regulations are more comprehensive, requiring judicial authorization for FGG and for covert DNA collection, limiting the types of crimes FGG may be used to investigate, requiring law enforcement to first pursue all reasonable leads, and using government DNA databases before seeking FGG authorization. The use of FGG in other states is unregulated.

The sensitivity of DNA profiling combined with the power of databases can lead to false accusations. For instance, despite having been in the hospital at the time of the crime, a California man was jailed for five months on a murder charge after his profile was selected from a database as matching one taken from the victim’s fingernail. It turned out that the oxygen sensor EMTs placed on the victim’s finger had previously been used by the same EMTs to measure the arrestee’s oxygen. Studies have shown that DNA is easily transferred from objects a person touched to objects a person never touched, including clothes that are washed together. This means that it is important that defense attorneys investigate how the source DNA may have gotten to the crime scene. This includes the possibility that it was deposited long before the crime occurred as there is currently no way to determine when DNA was left on an object or person.

A defense attorney contemplating a challenge to FGG must become familiar with how it was used in their case, using the tools of discovery. Important information to be sought includes what traditional methods were used prior to FGG and how the FGG profile was generated.

Generally, defense counsel should seek information on validation studies and the accuracy and limitations of the methods that were used. Any reports generated by the labs and genealogists should be requested.

Further, forensic samples are often degraded and/or mixtures. Degraded samples require additional processing and amplification due to low quality. This increases the likelihood of lab errors. Mixtures can implicate other suspects and are another source of potential lab error. Thus, it is important to determine whether the sample was degraded or a mixture and whether only one or several DNA profiles were generated from crime scene DNA samples.

If there was more than one profile, information on the other profiles should be requested, including whether they were identified or investigated as suspects and how many cMs they had compared to the crime scene sample. This is to determine whether law enforcement was subject to confirmation basis, using FGG to confirm what they already believed instead of using FGG to identify potential suspects.

There have been few defense challenges to FGG. This may be due to the fact that the collection of samples from arrestees for CODIS-like DNA profiling and entry into a database has long been upheld by the highest courts. See Maryland v. King, 569 U.S. 435 (2013). Although several states disagree on the point and provide greater privacy protection for its citizens (see e.g., State v. Wright, 961 N.W.2d 396 (Iowa 2021) – covered in the January 2022 issue of CLN), most states and the federal courts have held that no warrant is required to covertly seize a suspect’s trash and use DNA from it for CODIS-like profiles. Most courts cite California v. Greenwood, 486 U.S. 35 (1985), for the proposition that there is no subjective expectation of privacy in trash once it is deposited for collection outside the curtilage of a home, and thus, police are permitted to seize and search it without a warrant. Recently, a Texas appellate court held that defendants lack standing to challenge FGG DNA testing of abandoned property. McCurly v. State, 653 S.W.3d 477 (Tex. App. – Ft. Worth 2022).

Despite those cases, the highest appellate courts have yet to address the issue of covert discarded DNA collection for FGG profiling. This remains an open question because of the wealth of information FGG profiles contain and reveal. The U.S. Supreme Court has traditionally measured privacy interests by the amount of information revealed and recently held that a warrant is required for law enforcement to obtain cellphone location tracking information because of the wealth of information it provides. Carpenter v. United States, 138 S. Ct. 2206 (2018). The Carpenter Court reasoned that it did not matter that the information was obtained from a third party. FGG DNA profiles obtained from third party vendors contain much more intimate information than cellphone tracking. So presumably, a strong argument can be made for the necessity of a warrant for collection and testing regarding FGG DNA obtained from discarded items.

DNA database searches are also open to challenge as the kind of general warrant that is prohibited by the Fourth Amendment since they provide private information regardless of whether it is used or not. See Andersen v. Maryland, 427 U.S. 463 (1976); Coolidge v. New Hampshire, 403 U.S. 443 (1971). Like the original general warrants that led to the adoption of the Fourth Amendment, FGG searches specify only the offense, leaving whom to arrest and where to search to the discretion of the executing officials. See Steagald v. United States, 451 U.S. 204 (1981).   



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