The blog of the Urban Institute
August 9, 2012

DNA: The coming scientific revolution in policing

August 9, 2012

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.


As an organization, the Urban Institute does not take positions on issues. Experts are independent and empowered to share their evidence-based views and recommendations shaped by research.


A revolution? Maybe not the way you expect it. More of a revolt of civic liberty minded people! Didn't founding father Benjamin Franklin say something like ' people who trade liberty (which implies privacy) for security deserve neither and will loose both? As a European who was once an exchange student in the USA to learn about your values, it strikes me how 'un American' all this DNA hoarding is. It seems this DNA lobby is like any big business lobby. It is not ashamed to parade a few victims of horrific crimes to jerk the public's heart strings and so presenting DNA as a common-sense solution that shouldn't be derailed by the lingering concerns of liberal minded justice reformers and paranoid privacy advocates. I note Katies' parents the Sepichs do not allow any dissenting views to be heard on their 'Make DNA law' web page. My heart goes out to them for their loss but it has made them blinkered DNA hoarding advocates who are abused by an entire industry getting rich on selling DNA test kits and selling our most private information to the highest bidders. Katie herself would turn in her grave, the way her memory is misused. Fact is all biometric identity systems become less effective the more records you load in them. They become diluted, as more marginal criminals — or even innocent people — are included in it. There are more opportunities for error; the larger the database gets, the greater the chances are of 'false positives' and partial matches with innocent people." If you don't believe me enter the search term 'Birthday Paradox' in WikiPedia. Lazy cops would rather listen to the DNA lobby and be hoodwinked in believing they can solve all these crimes without actually getting away from their desks and investigate.