Familial DNA Searching for Criminal Forensics: Q&A

When DNA evidence is collected at a crime scene, submitting the sample for a search within a DNA database does not always identify a profile match. There is a way to extend that search and generate leads, called familial searching (FS). FS is used to identify close biological relatives of an unidentified DNA profile obtained as evidence. The basic premise is that DNA profiles of immediate family members, such as siblings, parents, or children, are likely to have more alleles in common than unrelated individuals. These familial profile matches can generate new investigative leads for law enforcement.

Currently, a few states are using FS under their state database laws, although none explicitly permit FS. Many agencies have yet to adopt policies related to FS, even though it has been found to be as effective as CODIS for identifying sources of evidence. The absence of clear ethical guidelines and policy regarding how to properly utilize FS prevents many local and state jurisdictions from adopting this investigational tool.

In order to address concerns and existing policies related to FS and to guide policy decisions by agencies implementing FS, the National Institute of Justice (NIJ) issued the report Familial DNA Searching: Current Approaches in January 2015. The goal of the report was to provide information to policy makers, law enforcement officials, forensic laboratory practitioners, and legal professionals about how FS is being applied within the criminal justice realm.

Mr. Rock Harmon, former prosecutor
Mr. Rockne Harmon, former prosecutor

Answers to the following questions about FS were provided by Mr. Rockne Harmon, a retired former prosecutor and member of the team that produced the report for the National Institute of Justice.

What is familial DNA searching?

Familial searching (FS) is an additional search of a DNA profile in a law enforcement DNA database that is conducted after a routine search fails to identify any profile matches. The FS process attempts to provide investigative leads to agencies engaged in the pursuit of justice by identifying a close biological relative of the source of the unknown forensic profile obtained from crime scene evidence.

In brief, how does it work?

Familial Searching is based on the concept that first-order relatives—such as a sibling or parent/offspring— often will have more alleles of their DNA profiles in common than those of unrelated individuals. FS involves a two‐phase process. The first phase of FS produces a candidate list from the DNA database ranked by likelihood ratio estimates supporting the specified relationship (i.e., parent– offspring and full sibling) compared with the alternate hypothesis of being unrelated. The second phase of the process typically uses additional genetic testing, such as analysis with lineage markers, usually Y‐ STRs, to confirm or refute the specified relatedness.

In what types of cases is familial DNA search most appropriate and effective?

Familial Searching is suitable for trying to produce investigative leads from biological evidence in any unsolved crime where that evidence is material. It is typically used for unsolved rapes and murders after the evidence profile has been uploaded to CODIS and no offender hit has been produced.

What states are currently using the technique?

Virginia, Colorado, Texas, California, Wyoming, Utah, Minnesota, Florida, Michigan

Have these states demonstrated success?

Yes, to varying degrees. An effort was made to calculate a success metric for Familial Searching using the same criteria that the FBI uses to calculate the effectiveness of CODIS. Of the 90 FS cases in Denver to date, 23 of the database searches resulted in identification of a true biological relative of the evidentiary sample (a success rate of approximately 26%). California’s success metric is 26/66, or 39%. This data suggests that FS can be at least as successful as CODIS is.

What are the legal limitations/ramifications?

There are none once it is determined that the existing state database law implicitly authorizes Familial Searching as all nine states have determined. There are no changes to anyone’s 4th Amendment rights inherent in FS.

What concerns may be preventing or slowing its use in the field?

Misconceptions and confusion abound! Questions about statutory interpretation are answered by scientists, not lawyers. Whether or not legislative changes are necessary are the principal subject of confusion. The fact that every state using FS found authorization in their existing database law is either unknown or of little concern.

Perhaps the biggest obstacle to FS is the shocking underutilization of Y-STRs in about half of the government labs in the US. While this inadequacy denies a valuable tool from law enforcement in those jurisdictions, its absence also dooms any future for FS because the Y-STR lineage testing is a vital major component of FS.

Are there ways to overcome these concerns?

Open, meaningful discussion among the labs, law enforcement, and knowledgeable prosecutors can easily inform and address any concerns.

What are the ramifications for law enforcement not being able to use Familial Searching to solve crimes in their jurisdictions?

Currently, there are approximately 326,000 unidentified forensic profiles in NDIS that have not been associated with aiding an investigation. If the success rate of FS is maintained at the same rate as that in Denver (26%), then one could expect FS to produce valuable investigative leads in about 84,760 additional cases.

Instead law enforcement has been turning to highly unproductive practices such as DNA dragnets, genealogy, pictures from DNA, and bio-ancestry information instead of having meaningful discussions about implementing FS.

What do you see for the future of familial DNA search?

Although the potential of Familial Searching has been demonstrated, interest in adopting FS appears to be waning.

While Familial Searching is a powerful tool that can help law enforcement identify suspects and solve crimes more quickly, its use raises many ethical questions. What guidelines do you think need to be in place if such a technique is used by law enforcement? We would like to hear your thoughts.

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Darcia Schweitzer
Darcia is a Content Lead at Promega. She earned her BS in Secondary Education at the University of Wisconsin Oshkosh, with minors in Biology and Spanish, and her MS in Biotechnology at the University of Wisconsin Madison. She is passionate about sharing scientific knowledge with all audiences, including her family and friends—whether they have solicited the lesson or not! In her free time, Darcia enjoys reading, playing volleyball, eating delicious food and cheering for the Chicago Cubs.


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