DNA: The coming scientific revolution in policing
DNA testing has been singled out among forensic practices as being exceptionally accurate. So why hasn’t it assumed its rightful place as the premier forensic tool in the criminal justice arsenal? Because, despite the promise of DNA analysis, few law enforcement agencies are using it to help identify unknown suspects.
In a landmark 1961 case, Mapp v. Ohio, the U.S. Supreme Court held that evidence collected in violation of the Fourth Amendment, which protects against unreasonable search and seizure, was not admissible in court. Subsequent cases expanded the so-called exclusionary rule to include evidence collected as a result of illegally obtained evidence. This holding is often cited as the cause of the first revolution in policing. Ad hoc policing went the way of the Edsel, and a new era of professional policing began. A byproduct of the new procedural rules was a greater reliance on forensic evidence to make a case.
In 2009, the National Academy of Sciences released a study that was critical of the basic science behind many forensic practices. We’ve known for years that some of the most routine ways of identifying suspects, including eyewitness testimony and jail house snitches, were dubious. Now, we can add forensic evidence—ballistics, impression evidence (footprints and bite marks), analysis of trace evidence (hair and fibers), and perhaps even fingerprints—to the list.
The National Academy did not conclude that these types of forensic evidence routinely implicate the wrong suspect. Rather, it concluded that these techniques include an element of subjectivity that leaves their conclusions suspect. That subjectivity means that experts cannot determine the probability of a match or guarantee that results are reproducible. Traditionally, courts have allowed this evidence to be considered on the grounds that the forensic experts who testified were credible and that the science was generally accepted in the scientific community. The National Academy recommended that the standards be raised both for expert qualification and for the underlying science.
The Academy, however, singled out DNA evidence as an exceptionally accurate means of identifying suspects. Our work has shown that it is also cost-effective. We found that using DNA evidence to investigate high-volume crimes leads to more than twice as many suspect identifications, twice as many arrests, and more than twice as many cases accepted for prosecution.
American policing seems poised for a second revolution, as widespread adoption of DNA collection and analysis ushers in the era of scientific policing. The reality, however, is that the use of DNA evidence is growing much more slowly than its potential. While glamorized in the popular media, DNA analysis remains a rarely used tool of law enforcement. For comparison, since 2001, more than 10 million Americans have been the victim of a violent crime, more than 15 million Americans have experienced a burglary and felt the sanctity of their home trampled, and 10 million cars have been stolen. In the most recent data from the FBI, only 175,000 investigations have been aided by DNA.
Currently, burglaries and other costly high-volume crimes receive scant attention from police and prosecutors—even though burglars may also commit violent crimes—because they are extremely hard to solve. With enough police and laboratory resources to use DNA in all property-crime investigations, Americans could expect stunning results. In one year, police could identify suspects in more than 300,000 residential burglaries nationwide that would otherwise go unsolved and they could make 200,000 additional arrests. Hundreds of thousands of other crimes, such as motor vehicle theft, could be solved as well. As an added bonus, many more serious offenders would be caught in the process.
Creating the infrastructure to do this will require a substantial investment. Creating the evidence collection and laboratory capacity necessary to process all this evidence will cost billions. Fortunately, this investment is stimulating to job growth—the current demand for forensic scientists and technicians far exceeds the supply.
The second revolution in law enforcement is coming, and public safety will be far better protected if we get ahead of the wave and adequately equip a new generation of police. The challenge is how to finance the infrastructure necessary to allow the revolution to occur.
Tomorrow: how to encourage private financing of public sector activities.