DNA of Criminals' Kin Cited in Solving Cases
Friday, May 12, 2006
Cops would solve more crimes if they expanded their use of the nation's DNA fingerprinting system to test close relatives of known criminals, according to a research report that raises novel and difficult civil liberties issues.
The proposed crime-control strategy, already in growing use in Britain, is based on two central facts: Close relatives of criminals are more likely than others to break the law, research has shown, and, because those individuals are related, their DNA "fingerprints" will be similar. That suggests that if police find a crime-scene specimen with a DNA pattern close to -- but not exactly the same as -- that of a known lawbreaker, a relative of that known criminal may be the culprit.
In Britain, where rules governing the use of DNA for fighting crime are more permissive than in most U.S. states, the approach has been used dozens of times and has helped solve several cases, said Frederick R. Bieber, a Harvard medical geneticist who led the new study with colleague David Lazer and Charles H. Brenner of the University of California at Berkeley.
In one recent case, for example, a specimen from a 1988 murder scene was found to have a DNA pattern similar to that of a 14-year-old boy whose DNA was on file with the police. Investigators obtained a sample from the teenager's uncle, which perfectly matched the crime scene specimen and led to his conviction.
The new analysis, published yesterday in the online edition of the journal Science, is the first to use sophisticated computer models to predict just how useful such "familial" searches may be.
The computation is based on well-established facts -- such as the prevalence of certain DNA variants in the population -- and less precise assumptions, such as the odds that a criminal has a close family member whose DNA is already on file.
In the United States, those odds are rather high: A 1999 Justice Department survey found that 46 percent of prison inmates had at least one sibling, parent or child who had been incarcerated at some point.
All states take DNA from all convicted felons, and many get specimens from a wide range of others.
Using conservative assumptions, Bieber and his colleagues calculated that U.S. law enforcement authorities could increase their "cold hit" rate (the percentage of DNA searches that result in perfect matches) by 40 percent if they were to check the DNA patterns of criminals' family members when searches generate near misses.
Cold-hit rates vary widely today. Assuming they average about 10 percent, Bieber said, a 40 percent increase would bump that rate up to 14 percent.
"This is proof of concept that existing methods of kin analysis could be used in forensic analyses with an expectation of success in a fair proportion of cases," said Bieber, who is to present the findings tomorrow at a meeting of the American Society of Law, Medicine & Ethics in Boston.
The approach raises hackles among many civil libertarians, who note that Britain does not have a Bill of Rights. Under the Fourth Amendment, U.S. authorities are generally required to show compelling evidence that a person has committed a crime before they can demand a DNA sample.
"If I give up a sample, does that mean I've also committed all my blood relatives to a search?" asked Carol Rose, executive director of the American Civil Liberties Union of Massachusetts. "That's where the technology is moving faster than the law."
Familial testing would also amplify racial inequities in the criminal justice system, which already focuses disproportionately on blacks, said Troy Duster, a New York University sociologist.
In the United States, where the DNA fingerprints of about 3 million people are stored in a national criminal database, familial testing has only rarely been acknowledged. Tom Callaghan, custodian of that database, said the FBI, which handles federal cases and those in the District, does not pursue partial matches.
But no state is precluded by law from using the approach. And at least two -- New York and Massachusetts -- have statutory language expressly allowing it.
A few years ago, DNA from a specimen saved from a 1984 North Carolina rape and murder was compared against that state's database and was found to be very similar to the pattern of a man whose DNA was on file. Police trailed the man's brother and performed a DNA test on a cigarette butt the brother discarded. When the pattern was found to match the crime specimen's exactly, the brother confessed and was convicted.
Bieber acknowledged that the strategy could impinge on civil liberties.
"It's a balancing act," he said. "But I think we are duty-bound to explore the potential."