College of American Pathologists



Parentage Testing Used to Solve Difficult Crimes

Posted June 1, 2011

Colin C. Pritchard MD, PhD
Junior Member of the CAP Histocompatibility and Identity Testing Committee

Be careful what you do with your pizza. In July 2010, Los Angeles police arrested Lonnie D. Franklin Jr. as a suspect in the “grim sleeper” serial murders based on testing using DNA recovered from a piece of discarded pizza. Police had begun 24-hour surveillance of Mr. Franklin after familial searches of a DNA database linked Mr. Franklin’s son, Christopher Franklin, to DNA recovered from the old murder scenes. Christopher Franklin had a DNA sample taken recently for entry into the DNA database as part of a felony weapons charge. Detectives performed a search of the DNA database to specifically look for family relationships to the DNA profile obtained from evidence in the old serial murders and discovered that Christopher was likely to be a direct relative of the serial killer. The elder Franklin fit the killer’s demographics and lived in close proximity to where the murders took place, which prompted the stakeout culminating in the DNA match established by the discarded pizza slice.

This case was reported in a high profile July 8, 2010, New York Times article, entitled “‘Grim Sleeper’ Arrest Fans Debate on DNA Use,” that emphasized both forensic utility and privacy concerns.1 It is the one of the first times that familial searching has been used to successfully solve a crime in the United States (the technique has been widely used in England). The practice is currently legal only in Colorado and California.

Forensic pathologists and law enforcement have long used DNA testing to identify criminals through exact matches of evidentiary DNA profiles against those from reference samples. The technique involves PCR amplification of at least 13 short tandem repeat (STR) loci that forensic laboratories around the world have standardized as a DNA test panel. These loci have been carefully selected to be highly polymorphic between individuals, but not to have any known disease association. An exact match at all STR loci between evidence and reference profiles conveys near certainty that the samples came from the same source. DNA testing for family relationships uses the same methodology, but the analysis is complicated by the fact that generally only a single allele is shared between parent and child, reducing the discriminatory capability of the assay. This limitation reduces the probability of exclusion resulting in a higher rate of false-positives. For example, one study found that one of 249 known nonrelatives was falsely predicted to be a child’s father with a probability of 99.72% based on a panel of 15 STR markers.2

Due in part to the limitations of parentage testing discussed above, the inability to assign family relationships with 100% certainty, and inherent privacy concerns, most states still do not allow familial searches of DNA databases of convicted felons. Opponents have also argued that the technique is a form of racial profiling because of the disproportionate number of African Americans present in law enforcement databanks.3 The arrest of Lonnie D. Franklin Jr. is a dramatic example of the power of a familial search to solve a murder case that otherwise may never have been solved. The success of this strategy is likely to lead more states to consider legalizing familial searches in specific circumstances. DNA testing by PCR for family relationships is one of many emerging technologies used by pathologists in diagnostic medicine. Pathologists with expertise in DNA parentage testing are excellent resources for medical clinicians to outline the advantages and potential pitfalls of forensic familial searching.


  1. Steinhaur J. ‘Grim Sleeper’ arrest fans debate on DNA use. New York Times Online. July 8, 2010. Accessed April 29, 2011.
  2. Twelfth International Symposium on Human Identification. Genetica DNA Laboratories, Inc., October 9–12, 2001.
  3. Rosen J. Privacy risks and racial bias. New York Times Online. Updated July 15, 2010. Accessed April 29, 2011.

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