The high profile case concerning the arrest of Lonnie Franklin – aka The Grim Sleeper – in 2010 drew nationwide attention to a new tool in the DNA forensics arsenal: familial searching. This tactic is used when an unknown sample does not fully match anyone in a DNA database, but may partially match a known profile in a manner that may point to a close relative being the culprit.
The state of California has developed rather stringent guidelines for the use of familial testing that seem prudent. But a recent paper by Rori Rohlfs et. al. in PLOS ONE suggests that despite these guidelines, real concerns still remain. The study, which The Los Angeles Times covered in a news story, found that the methods currently in use misidentify distant relatives as being more closely related to the unknown sample than they actually are, potentially subjecting them to unwarranted police scrutiny.
The abstract explains:
Although the California familial search policy is likely to identify a first degree relative if his profile is in the database, and it poses little risk of falsely identifying an unrelated individual in a database as a first-degree relative, there is a substantial risk of falsely identifying a more distant Y- haplotype sharing relative in the database as a first-degree relative, with the consequence that their immediate family may become the target for further investigation. This risk falls disproportionately on those ethnic groups that are currently overrepresented in state and federal databases.
In other words, a partial match between a crime scene DNA sample and a profile in the DNA database might mistakenly suggest that the two people are siblings or father and son, when in fact they are much more distantly related. That could result, in a hypothetical example, in a police investigation of a second cousin who doesn’t even know the suspect whose DNA was found at the scene of a crime.
Click here to read the entire paper. The authors also prepared two videos to accompany their study. One is a clear technical summary – in three and a half minutes – of the paper’s methods and findings. The other is a wonderfully innovative dramatization of three high school students discussing familial DNA searches and their pitfalls, with narration by Cephus Johnson, the uncle of Oscar Grant.