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The state of California has been a leader in the use of familial DNA searches -- investigations that seek out crime suspects by taking unidentified crime scene DNA, looking in a state DNA database for people who are partial matches to that sample, and then track down those close relatives of the suspect to help chase down the ultimate target. A familial DNA search helped police nab 'Grim Sleeper' suspect Lonnie Franklin Jr. in 2010.

By and large, according to a report released Wednesday, California's system hits the mark: It finds parents, children and siblings in the database dependably, and it's unlikely to match a sample with a completely unrelated person. But in some cases, the analysis further suggested, the state's methods could falsely identify more distantly related people -- cousins, half-siblings, and the like -- as first-degree relatives.

That could mean that immediate family members of these mistakenly identified distant relatives could be targeted for further investigation, UC Berkeley postdoctoral fellow Rori Rohlfs and colleagues wrote, in a study in the journal PLOS ONE. That raises privacy concerns, especially...