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Familial DNA Testing Scores A Win In Serial Killer Case

Publication Date: 
July 16, 2010
Greg Miller

Professor Hank Greely, an expert on law and the biosciences, is quoted on controversy around using familial DNA evidence to solve crimes. Greg Miller of Science Magazine filed this story:

A quarter-century of conventional detective work failed to track down the killer responsible for the deaths of at least 10 young women in south Los Angeles dating back to the mid-1980s. But a discarded piece of pizza and a relatively new method of DNA testing has finally cracked the case, police announced last week. On 7 July, L.A. police arrested Lonnie Franklin Jr., 57, a former garage attendant and sanitation worker they suspect is the serial killer nicknamed the "Grim Sleeper."

Since 2008, California has allowed so-called familial DNA searches, in which investigators look for close but not exact matches between DNA evidence collected at crime scenes and the state's data bank of DNA collected from 1.3 million convicted felons. The method has a longer history in the United Kingdom, where it led to a conviction in a murder case in 2004. In Colorado, the method led to a guilty plea in a car-theft case in Denver last year.


"I think it's great that this tool was used to catch this defendant," says Hank Greely of Stanford Law School. But he cautions that the method does have downsides. His research suggests that in a database with DNA from a million individuals, hundreds or even thousands of people might have a close enough match to suggest a blood relationship, depending on the strictness of the test and the rarity of the genotypes being tested. If those matches cast suspicion on innocent people, the burden would fall disproportionately on African Americans, who are overrepresented in the U.S. prison population. "It does raise some concerns about discrimination," he says.