The Los Angeles case “shows why it can be tremendously useful in cases that seem pretty dead and hard to crack,” said Jennifer Mnookin, a law professor and evidence expert at the University of California, Los Angeles. “So therefore we will very likely see an increasing use of these techniques, and at a minimum one hopes it is done in a sensitive way that is thoughtful and attentive to the concerns” of its critics, she said.

At least some of those critics remain skeptical.

“Familial searching is a tool, and at this point it is a very imprecise tool,” said Michael Risher, a lawyer with the American Civil Liberties Union of Northern California, who added there was the possibility of innocent people being harassed in the pursuit of a crime. “It has the potential to invade the privacy of a lot of people,” he said.

Many law enforcement agencies collect DNA samples of convicted felons in hopes that DNA from other crime scenes can be matched to those individuals.

In the case of a close but imperfect match between crime scene DNA and that of someone locked up, forensic scientists say, the person responsible in that crime may well be a relative of the person locked up. Through a software tool, scientists are then able to painstakingly parse the DNA to determine sibling or parent-child relationships, information the police use to pursue possible suspects.

While the practice is common in England, it has been limited largely to Colorado in the United States. But in 2008, the California Department of Justice began using familial searches  in the face of significant protests  to solve hard crimes. The state restricted the practice to major, violent crimes in which all other investigative techniques had proved fruitless.

Those who oppose the technique argue that there are inherent privacy concerns, and that it serves, in essence, as a form of racial profiling because a higher proportion of inmates are members of minorities.