In Fighting Crime, How Wide Should a Genetic Net Reach?

It's the latest criminal investigation technique, and it gives new meaning to that old saw "the ties that bind."

Recently, forensic scientists in California used a genetic analysis procedure called "familial searching" or "kinship searching" to help the police identify a suspect in the "Grim Sleeper" serial murder case - and they did so by using a DNA sample collected for another purpose from the suspect's own son. The Los Angeles police later arrested the father, Lonnie David Franklin Jr., who has since been charged with 10 counts of murder.

Forensic scientists routinely use a standard search method to try to identify a suspect who has left bits of DNA at a crime scene. They use a computer analysis to compare DNA from the scene to DNA profiles of known convicted offenders stored in a state database. When the profiles match exactly, genetic analysts call it a "cold hit."

But the Grim Sleeper case (so named because of an apparent hiatus in a killing spree that dates back to 1985) is unusual because, after regular searches came up empty, officials...