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Familial Searching: Extending the Investigative Lead Potential of DNA Typing

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Bruce Budowle

Institute of Investigative Genetics, Department of Forensic and Investigative Genetics, University of North Texas Health Science Center, Fort Worth, Texas

Publication Date: 2010

DNA typing is an invaluable forensic tool for associating biological evidence with its true source. Generally DNA technology affords the forensic scientist the ability to effectively eliminate individuals who have been falsely associated with a biological sample and to substantially reduce the number of potential contributors to a few (if not one) individuals. When it was initially developed, DNA typing was used predominately to compare an evidence profile directly with the profile from a reference sample(s). Many of these one-to-one comparisons have been extremely useful in assisting to solve crimes. More than a decade ago the capability of DNA typing was substantially expanded by the creation of DNA databases that contain profiles from convicted felons (and now arrestees as well) and profiles from evidence from unsolved cases(1) (2) . The DNA profiles contained within the forensic indices can be compared, and candidate matches can be investigated further. Indeed, DNA database searching has become another routine way to develop new and often strong investigative leads. The success stories of DNA database search leads are well known for identifying suspects (ultimately perpetrators) and are being used increasingly in post-conviction exoneration cases.

Initially, database searching was applied to direct profile comparisons to generate investigative leads. However, in 2003–2004 the Forensic Science Service demonstrated that the database searching capabilities could be expanded by employing indirect comparisons via an approach known as familial searching(3) . This type of search led to the identification of Craig Harman through an association with a first-order relative’s DNA profile housed in the United Kingdom DNA Database. The crime involved the heart attack death of a motorist due to a brick thrown through the windshield of the victim’s truck from a bridge above the roadway. A direct comparison of the DNA profile from the brick and profiles in the National Database did not result in any candidate matches. However, 25 similar DNA profiles were identified, and at the top position on the list of candidates was a relative of Craig Harman. Harman voluntarily submitted a reference sample, and his DNA profile was a direct match with that of the evidence. He subsequently pleaded guilty to manslaughter.

"There is good a priori reason to believe that familial searching would have some success. According to the Bureau of Justice Statistics Correctional Populations in United States, 1996 report, at least 42.8% of inmates had close relatives who also have been incarcerated."

Anecdotally, familial searching had been carried out previously to the Harman case for years in one-to-one comparison cases in which an evidence profile was sufficiently similar to the evidence. Such similarities often prompted the forensic scientist to suggest to investigators to look for a relative of the suspect. However, the Harman case was the first one in which a DNA database was used to develop the investigative lead. Today there are a number of documented cases where familial searching was successful in identifying the perpetrator(3) (4) .

Familial searching is based on the principle that first-order relatives, i.e., siblings, parents, and to a lesser degree even more distantly related relatives (e.g., uncles, aunts and cousins), will share features of their DNA profiles (i.e., alleles) on average more so than do unrelated individuals. While there may be no direct matches when comparing an evidence DNA profile with reference profiles in a DNA database, there can be "near genetic matches" (or better stated "associations") with convicted felon profiles, and one of these candidates may be a close relative of the true source of the crime scene evidence. Familial searching is another tool in the arsenal for developing investigative leads from DNA databases.

There is good a priori reason to believe that familial searching would have some success. According to the Bureau of Justice Statistics Correctional Populations in United States, 1996 report(5) , at least 42.8% of inmates had close relatives (i.e., father, mother, brother, sister, child) who also have been incarcerated. Since DNA profiles of most inmates are entered in the CODIS system (and, for example, the UK Database), familial searching has a great potential to assist law enforcement by identifying an individual in CODIS who may be a close relative of the true source of a forensic sample. Typically, familial DNA database searches are best suited for identification of an individual who could be a sibling of the true source of the evidence sample and identification of an individual who could be the parent or offspring of the true source of the evidence.

Use of familial searching can constitute a powerful law enforcement tool that should increase the number of suspects (and thus perpetrators) identified through forensic DNA technology, and advocates say it already is a legitimate way to develop investigative leads(3) . Anecdotally, it appears that the use of familial DNA searching in the UK that results in a conviction may be on a performance par with the use of CODIS to produce offender hits that result in conviction(3) . Bieber et al.(4) suggested that familial search analysis could increase the cold hit rate up to 40%. Even with its success in identifying true perpetrators via indirect associations in a DNA database search, familial searching is not without its critics, who contend that familial searching simply is an invasion of privacy and merely a genetic fishing expedition by law enforcement. While those against familial searching acknowledge that convicted criminals should lose some privacy rights, they assert that relatives of convicted felons do not have an expectation of a reduced right to privacy. Critics claim that these searches are even more troubling since they constitute an increased discriminatory scrutiny of the low-income and ethnic groups that are overrepresented in the database(6) .

The recent identification in California via familial searching of a serial killer suspect shows that this investigative tool could be beneficial to underprivileged groups(7) (8) . For more than 30 years, a serial murderer—the Grim Sleeper—in Los Angeles remained unidentified. The majority of victims were young African American females (that clearly represented a low-income, minority population group). Yet familial searching linked Franklin via his son who was entered into the California database for a felony weapons charge in recent years. To ensure that the association was a viable lead, the DNA laboratory also typed the evidence and the son for Y STRs. Barring mutation, a father passes his Y STR chromosome intact to his son. Given the discrimination power afforded by current Y STR profiling kits is around 0.999, most false indirect associations can be eliminated(9) (10) (11) . Thus, when using a Y STR match threshold, rarely would an investigator be incorrect in following up the lead provided by the DNA association. The two Y STR profiles were the same, which strongly supports a paternal relationship between the source of the DNA evidence and Franklin's son. Franklin's DNA profile was a direct match to evidence in the murders over the past three decades. This is strong support of the power of Y STRs in this context.

Even with this success story the debate on the use of familial searching will likely continue. Currently some countries and only two US states (California and Colorado) are openly conducting familial searching; few jurisdictions are moving towards conducting familial searching, and one state (Maryland) has prohibited familial searching of criminal databases. As the debate continues additional questions will likely arise, including:

  1. Could one make a proportionality argument and that the seriousness of the crime warrants its use (for example in the Grim Sleeper case)?
  2. Alternatively to the proportionality position, if it is acceptable under serial murder cases, should familial searching be appropriate in other “lesser” crimes? After all there is evidence that a large portion of violent criminals start out by committing lesser crimes.
  3. Should familial DNA searching be made available to a convicted person who has been afforded post-conviction DNA testing that has not yet “exonerated” him/her because the identity of the source of the forensic unknown DNA profile has not been established, even after a CODIS search?
  4. Is familial searching any different than using partial information as is done in other settings?
  5. Does the aura of DNA impede its use—i.e., should DNA be treated differently than other forensic evidence?
  6. Is a one-to-one comparison case in which a familial association is indicated any different than a familial association obtained by a database search?
  7. Is legislation required prior to proceeding with a familial search?
  8. Is there accountability if a CODIS manager or a laboratory analyst discovers a potential suspect who partially matches the evidence and does not report the finding?
  9. Could the nonreported association constitute Brady material?
  10. What about the next victim who would not have become a victim if the analyst provided the information?
  11. Should database managers seek legal advice on what is proper action regarding partial matches or potential associations?
  12. If a state or jurisdiction desires to implement familial searching, what are the best practices to apply?

With regard to the last question, software is needed that effectively searches databases based on the best-performing parameters. The proposed practices for identifying associations with their false-positive and false-negative rates should be understood(12) . When possible, Y STR typing should be performed (for male relatives)(11) .

In conclusion, there is unequivocal evidence that familial searching will increase the cold hit rate and help solve more cases. Most states legislatively authorized CODIS to be utilized for "criminal identification" purposes. The means used to achieve that purpose are seldom specifically described in the empowering statutes. California and Colorado each implemented familial DNA searching without legislative assistance(3) (13) . The "Grim Sleeper" case shows that familial DNA searching can be used solely for "criminal identification" purposes (see reference 20 for an extended discussion of this topic(14) ). The prediction is that as more successes such as the Grim Sleeper case are reported, more laboratories will seek to use familial searching. If familial searching is to be implemented it should be performed in a well-thought-out, robust manner. There are some models to follow, and the laboratory should work closely with its legal counterparts to develop an effective plan.

Editor's Note: Learn more about familial searches to solve crimes at the 21st International Symposium on Human Identification, which is being held October 11–14, 2010, in San Antonio, Texas. A panel discussion on October 14 will explore the details of familial searching and focus on the controversy behind the policy. Panelists will include Bruce Budowle, Institute of Investigative Genetics; Rockne Harmon, Alameda County District Attorney’s Office (retired); Jennifer Luttman, Federal Bureau of Investigation; Chris Maguire, Forensic Science Service; and Sonia Suter, George Washington Law School.


  1. Budowle, B. et al. (1998) CODIS and PCR-based short tandem repeat loci: Law enforcement tools. In: Proceedings of the Second European Symposium on Human Identification 1998, Promega Corporation, Madison, Wisconsin, 73–88.
  2. Martin, P.D., Schmitter, H. and Schneider, P.M. (2001) A brief history of the formation of DNA databases in forensic science within Europe. Forensic Sci. Int. 119, 225–31.
  3. Morrissey, M.R. (2010) Familial DNA database searches.
  4. Bieber, F.R., Brenner, C.H. and Lazer, D. (2006) Finding criminals through DNA of their relatives. Science 312, 1315–6.
  5. Bureau of Justice Statistics (1996) Correctional Populations in the United States, 1996
  6. Mnookin, J. (2007) Issues facing partial DNA matches in criminal investigations.
  7. L.A. Times (2010) Pizza slice helped link suspect to Grim Sleeper serial killings, sources say.
  8. L.A. Times (2010) In Grim Sleeper case, a new tack in DNA searching.
  9. Budowle, B. et al. (2009) Texas population substructure and estimating the rarity of Y STR haplotypes in forensic analyses. J. Forensic Sci. 54, 1016–21.
  10. Budowle, B. et al. (2009) The effects of Asian population substructure on Y STR forensic analyses. Leg. Med. (Tokyo) 11, 64–9.
  11. Budowle, B. et al. (2006) Clarification of statistical issues related to the operation of CODIS. Seventeenth International Symposium on Human Identification 2006, Promega Corporation..
  12. Ge, J. et al. (2010) Comparisons of the familial DNA database searching policies. J. Forensic Sci. (submitted).
  13. Steinberger, E. and Sims, G. (2008) Finding criminals through the DNA of their relatives—familial searching of the California offender DNA database. Prosecutor’s Brief XXXI (1–2) 28–32.
  14. Harmon, R. (2009) Familial DNA searching to solve unsolved crimes.

How to Cite This Article

Budowle, B. Familial Searching: Extending the Investigative Lead Potential of DNA Typing. [Internet] 2010. [cited: year, month, date]. Available from: http://www.promega.com/resources/profiles-in-dna/familial-searching-extending-the-investigative-lead-potential-of-dna-typing/

Budowle, B. Familial Searching: Extending the Investigative Lead Potential of DNA Typing. Promega Corporation Web site. http://www.promega.com/resources/profiles-in-dna/familial-searching-extending-the-investigative-lead-potential-of-dna-typing/ Updated 2010. Accessed Month Day, Year.

Contribution of an article to Profiles in DNA does not constitute an endorsement of Promega products.

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