Harmless Error or Unfair Prejudice? An Early Assessment of Genealogy in the Criminal Legal System

The Fourth Amendment ordinarily protects against warrantless, unreasonable searches and seizures, and the court relies on the defendant’s justifiable expectation of privacy in evidentiary hearings. While advancements in technology and surveillance have not superseded the Fourth Amendment, their involvement in the criminal legal system distort the Amendment’s “reasonability” factor despite there being a presumption against warrantless searches.

Investigative Genetic Genealogy (IGG) is an emerging investigative tool that combines advanced DNA analysis and genetic genealogy—the use of DNA testing to trace familial and ancestral relationships. IGG enhances law enforcement operations through identifying possible genetic and familial matches, such as close relatives, to DNA found at crime scenes. This data provides a clear analysis of familial lines that are often necessary when working with unidentified suspects or remains. Unlike traditional investigative methods, IGG is enabled by widely available direct-to-consumer genetic testing (DTC-GT) databases that house a larger population sample than law enforcement sources. These are privately owned and operated companies that perform genetic testing and ancestry matches with obscure policies on access to critical DNA information, including access for law enforcement matters without a warrant. Accordingly, IGG stands to become a prevailing and potentially authoritative investigative method in the absence of a clear legal framework for genetic information sharing between DTC-GT companies and criminal investigators.

Historically, DNA searches in criminal investigations have been entered into the Federal DNA database, commonly known as the Combined DNA Index System, or “CODIS,” which consist of DNA profiles from participating federal, state, and local forensic labs. DNA samples and profiles from other crime scenes, convicted persons, and previous arrestees are housed in CODIS, and identifications are made by matching DNA from the crime scene to existing DNA from CODIS. Recently, criminal investigators have been turning to the use of IGG more often, already having used it to solve multiple infamous cases that had previously gone unsolved.

In April 2018, IGG was credited for its apparent identification of the Golden State Killer, (GSK) a former California police officer who would later confess to 13 murders and over 50 home invasion rapes that occurred between the 1970’s and 1980’s. For decades the GSK was not known to authorities who largely relied on traditional DNA searches in CODIS, until an investigator used a commercial database to identify a possible familial match which ultimately lead to the arrest, confession, and subsequent closure of the high profile cold case. Prior to identifying the GSK, however, police misidentified the suspect twice. While the wrongfully identified men were ultimately found innocent, this was after their DNA was collected and compared to the crime scene sample. Additionally, in December 2022, IGG was also used to identify Bryan Kohberger, a suspect in the Idaho college murders. In January 2025, Kohberger challenged the constitutionality of IGG’s use in the case, although the judge would later deny the motion to suppress the genetic information citing no violation of the Fourth Amendment and a lack of authority for Kohberger’s position.

While the GSK case resulted in a guilty plea, the initial misidentification of two innocent men calls into question the existence of appropriate safeguards for powerful investigative tools like IGG, which could become the dominating force in future criminal investigations. Current federal laws protecting genetic information include the Genetic Information Nondiscrimination Act (GINA) and the Health Insurance Portability and Accountability Act (HIPAA), but they lack needed protection against potential violations of IGG by law enforcement. Similarly, DTC-GT companies benefit from secondary usage of DNA after providing services, leaving sensitive genetic information open for continued third party use, like criminal investigations because of obscure policies lacking proper informed consent. Following the GSK result, the Department of Justice (DOJ) 2019 interim policy created the first comprehensive guidance for all federal law enforcement and grant-funded agencies on the use of IGG. The interim policy permits IGG usage as an alternative method after exhausting CODIS and all other available techniques for use in unsolved homicides, sexual assaults, and identification of human remains. However, as of October 2025, the DOJ policy has not been finalized, despite a self-imposed deadline to do so by 2020, and Department guidance may be subject to change.

In Kohberger’s case and in light of DOJ interim guidance, which is non-binding, IGG seems to circumvent the Fourth Amendment with an oversimplified application of the third-party doctrine and low bar for informed consent. The third party doctrine, which states that information no longer enjoys a reasonable interest in privacy if it has been shared to even one person, is overbroad considering the “shared” information in this situation is familial DNA. Whether private, commercial genetic genealogy databases themselves permit law enforcement to access their data should not dictate what is reasonable under the Fourth Amendment, especially if these companies have been incentivized to share this information.

IGG appears to bypass the Fourth Amendment’s warrant requirement out of necessity when exigency is not a reasonable justification. The warrant requirement mandates that reliable facts are presented to a judge to show that evidence of a crime has occurred and that the evidence is at the location stated. It must also discuss, with specificity, the particulars of the place to be searched and the people or things to be seized. Ordinarily, an investigation should rely on IGG to generate leads and is likely only doing so because investigators cannot yet state the particulars.

As IGG continues to advance, practitioners are challenged with balancing the obvious utility of IGG-obtained DNA evidence and the necessary protection of constitutional rights, particularly in areas that lack precedent. Practitioners can scrutinize the legality of DNA evidence without destroying its validity by leaning on scientific evidentiary standards, the warrant requirement, and existing legal doctrines like “Fruit of the Poisonous Tree,” which makes evidence inadmissible if it was obtained through improper means. Justice Sonia Sotomayor has emphasized that a Fourth Amendment search occurs when the government “violates a subjective expectation of privacy that society recognizes as reasonable.” Consequentially, IGG evidence stands to be characterized as either a harmless error on appeal or the suppression of unfairly prejudicial evidence at trial.