When David and Dina Weller robbed yet another home in Denver in 2006, investigators traced the couple by analyzing saliva left on a cigarette butt at the crime scene. That DNA evidence connected the pair to a string of burglaries, and each got a 36-year sentence.
The payoff was immediate and huge: The annual burglary rate for the neighborhood they operated in fell 40%.
For years, DNA forensic techniques have largely been used for serious crimes such as rape or murder. Now they are also being applied to lesser felonies -- such as car theft and burglary -- often with dramatic results.
That success also poses a dilemma for cash-strapped police agencies and local governments: Is an expansive new high-tech infrastructure worth the price for solving relatively minor crimes?
Some think law-enforcement agencies have more pressing needs for such sophisticated sleuthing. "Many jurisdictions have a backlog for solving rapes and other violent crimes," and typically those should be tackled first, says David Lazer, a professor at Harvard's John F. Kennedy School of Government and an expert in the use of DNA for crime-solving.
Still, that hasn't stopped a five-city pilot project that revealed promising results earlier this week, notably that DNA evidence can significantly increase the chance of netting a burglar. Though burglaries and car thefts have dropped in many U.S. cities because of better policing and other measures, a study suggests that DNA evidence can make a huge difference in helping capture and convict those guilty of property crimes.
"We found that twice as many suspects were identified, twice as many were arrested and more than twice as many were prosecuted," says David Hagy, director of the National Institute of Justice, part of the U.S. Department of Justice, which funded the scientifically-conducted and randomized study.
Research suggests that habitual burglars commit on average more than 240 burglaries each year, and often don't stop there. "People committing serious crimes usually start on smaller ones. So through this process you can get these people identified and in the system earlier," says Steve Allison of the National Law Enforcement and Corrections Technology Center at the University of Denver.
The university recently teamed up with five regional Colorado law-enforcement agencies and a prosecutor to create a DNA lab that deals exclusively with property crimes. The latest statistics from the Federal Bureau of Investigation show property crimes, including burglary, larceny, motor-vehicle theft and arson, were down 1.1% nationally in 2007.
Britain was one of the first countries to embrace the broader use of DNA evidence. Its Forensic Science Service has even tested mobile vans that can analyze samples from a crime scene in six hours, far faster than a traditional lab. That may help quickly identify and nab a burglar still lurking in the vicinity. In some areas, police have given DNA swab kits to victims of hate crimes, in case they are spat on or otherwise attacked again.
Inspired by Britain's example, the Justice Department funded its project in Orange County, Calif.; Topeka, Kan.; Phoenix; Los Angeles and Denver. For the study, biological evidence was collected at as many as 500 burglary and similar crime scenes in each location, between November 2005 and July 2007. Detectives investigated half of the cases -- the control group -- by traditional means. The other half was investigated using DNA leads as well.
Two key results: DNA is at least five times as likely to result in a suspect identification compared with fingerprints. Plus, suspects identified by DNA were found to have at least twice as many prior felony arrests and convictions as those identified in the control group.
There are considerable hurdles to expanding the use of DNA sampling in crime fighting. Civil-liberties groups fret that the rapid growth in DNA databases -- which studies say include innocent people along with offenders -- threatens to erode citizens' privacy. And DNA-based investigations are expensive and require trained police and high-tech equipment.
"What kind of bang for the buck are you getting?" says Tania Simoncelli, science advisor to the American Civil Liberties Union. "It's not a responsible use of our resources."
Another problem is more mundane: logistics. In a typical investigation, experts take a DNA sample obtained from a crime scene and try to identify the culprit by matching the sample with DNA profiles already stored in a database from previous crimes. But in forensic labs nationwide, a crush of DNA samples has caused huge backlogs. In many states, Harvard's Mr. Lazer estimates that it takes four to six months from when a rape or murder is committed to when investigators run a DNA sample through the database.
In Denver, property crimes had risen 5% annually for several years before the project started. Since then, police say they have used DNA to trap 95 prolific burglars, leading to a 13% annual decline in burglaries in each of the last two years. DNA evidence also more than quintupled the rate of case prosecution.
Were other factors responsible for the decline? As it turned out, one of Denver's six police districts didn't get involved in the project, "and it was the only area where crime levels rose," says Mitchell Morrissey, the city's district attorney and an advocate of DNA-based technology.