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Familial Searching

Familial searching is an additional search of a law enforcement DNA database conducted after a routine search has been completed and no profile matches are identified during the process.

Familial Searching

Familial searching is an additional search of a law enforcement DNA database conducted after a routine search has been completed and no profile matches are identified during the process. Unlike a routine database search, which may spontaneously yield partial match profiles, familial searching is a deliberate search of a DNA database conducted for the intended purpose of potentially identifying close biological relatives to the unknown forensic profile obtained from crime scene evidence. Familial searching is based on the concept that first-order relatives, such as siblings or parent/child relationships, will have more genetic data in common than unrelated individuals. Practically speaking, familial searching would only be performed if the comparison of the forensic DNA profile with the known offender/arrestee DNA profiles has not identified any matches to any of the offenders/arrestees.

Familial searching is often confused with what occurs when a partial match results from the routine search of the DNA database. A partial match is the spontaneous product of a regular database search where a candidate offender profile is identified as not being identical to the forensic profile but, because of a similarity in the number of alleles shared between the two profiles, the offender may be a close biological relative of the source of the forensic profile.

While familial searching is now being performed in several jurisdictions in the United States, the United Kingdom has the most experience conducting familial searching of their National DNA Database. Since 2003, the UK has conducted approximately 200 familial searches resulting in investigative information used to help solve approximately 40 serious crimes (as of May 2011). The UK has developed detailed protocols for familial searches that include an approval process, considerations for prioritization, research of family history, and training of law enforcement officers. One of the key components responsible for the effectiveness of the UK’s system is that the search is not based upon genetics alone. Age and, more importantly, geographic location are combined with the genetic data to produce a ranked list of potential relatives of the unknown forensic profile.

In considering whether familial searching should be implemented in your jurisdiction, it is important to recognize that a relative must already be in the database in order for the search to identify them as a potential relative of the forensic profile. It should be noted that even if a relative is in the database, it is possible that the relative may not be included in the ranked list produced by the familial search. For example, California’s validation of their familial searching protocol showed that approximately 93% of fathers and 61% of full siblings were identified by their familial search procedure using the CODIS 13 core loci in searching a database of approximately one million DNA profiles (96% of fathers and 72% of full siblings were identified using 15 loci).[1] However, regardless of whether or not a relative is in the database, a familial search will always generate a ranked list of potential candidates for evaluation.

Familial searching is not currently conducted at the national level or performed by the National DNA Index System [see Federal Register Vol. 73, No. 238 (December 10, 2008, at page 74937)]. To evaluate the feasibility of familial searching at the national level, the FBI’s CODIS Unit sought input from the Scientific Working Group on DNA Analysis Methods (SWGDAM) on specific questions relating to the efficiency of kinship matching compared to counting shared alleles, false positives and optimal database size, and optimal number of ranked candidates for the 10 million DNA profile database. SWGDAM provided the CODIS Unit with the following recommendations: (1) the use of kinship LRs is the preferred method for familial searching; (2) ranked lists should be reviewed since the true relative is not always ranked as the #1 candidate, and additional filters should be used to reduce the number of false positives; and, (3) since it is difficult to establish a threshold ranking for review of a ranked list when searching a database of over 10 million records when additional filters of metadata, geography, and Y-STR testing may not be available, routine familial searching at the national level is not recommended at this time.[2]

While familial searching is not performed at the national level, the following states currently perform familial searching at the state level: Arkansas, California, Colorado, Florida, Michigan, Texas, Utah, Virginia, Wisconsin, and Wyoming.[3]

Familial searching can help solve certain cases when applied properly. States considering familial searching may wish to review the discussion topics below as a starting point. Additionally, the “Recommendations from the SWGDAM Ad Hoc Working Group on Familial Searching” provide more information on this topic, including an appendix on their familial searching studies.[4]

Discussion Topics for States Considering Familial Searching:


  • Consider the applicable state laws and regulations governing the DNA databasing program to determine the best legal approach. Because many state laws are silent on the issue of familial searching, it is important to have a full legal review to evaluate whether familial searching is authorized in your jurisdiction. Those states which have adopted or rejected familial searching have done so under a variety of authorities:
    • Several states perform familial searching with the approval of state officials—for example, California implemented its familial search program with the approval of the state attorney general. Other jurisdictions have implemented familial searching based upon an administrative determination or laboratory policy. Two jurisdictions, Maryland and the District of Columbia, currently prohibit, by law, the use of familial searching.


  • Staff
    • Implementation of a successful familial search program takes time and requires significant resources and staff. Personnel with an expertise in kinship comparisons are necessary. 
    • Consider forming a task force to review requests for familial searches as well as to evaluate the familial search results. Such a task force should include laboratory personnel as well as law enforcement personnel and/or prosecutors, who are authorized to access criminal history records for researching background information on potential candidates.
    • Because the results generated by familial searching are not the same as CODIS matches, it is important to train law enforcement personnel on the appropriate follow-up, including additional investigative work.
  • Software
    • The current version of CODIS software does not have the capability to efficiently search and return information for familial searching. The states that conduct familial DNA searches use specially-designed software (not CODIS) to conduct these searches.
    • As with implementation of any new software, validation is required before use of such software in laboratory operations. Any validation must be conducted in accordance with Standard 8 of the FBI’s Quality Assurance Standards.
    • Develop standard operating protocols (SOPs) for familial searching prior to implementation of a familial search program.
  • Policies and procedures should be developed and approved prior to implementation and address, at a minimum, the following:
    • Privacy considerations
    • Release of information
    • Criteria for familial search requests:
      • Types of crimes eligible for searching
      • Types of forensic DNA records eligible for searching
      • If all other investigative leads must first be exhausted
      • Approval by task force, board, laboratory management, etc.
    • Processes for familial search:
      • Type of DNA records to be searched (e.g., offenders only, offenders and arrestees)
      • Frequency of searches
    • Use of additional filters for search results (e.g., YSTR testing, metadata)
    • Reporting of search results

1 S.P. Myers, et al., “Searching for first-degree familial relationships in California’s offender DNA database: Validation of a likelihood ratio-based approach,” Forensic Sci. Int. Genet. (2010).

2 “Recommendations from the SWGDAM Ad Hoc Working Group on Familial Searching,” (2013), available at the SWGDAM website (www.swgdam.org).

3 Listing of states as of September 2015.

4 “Recommendations from the SWGDAM Ad Hoc Working Group on Familial Searching,” (2013), available at the SWGDAM website (www.swgdam.org).