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How DNA Databases Deter Crime

Criminals worry more about getting caught than about serving a long sentence.

Deterring crime one strand at a time. Photographer: Robert King/Hulton Archive

Reducing crime without relying on mass incarceration is a worthwhile and admirable goal. Locking up criminals costs taxpayers a lot of money, can damage the communities of those sent away and is less than optimal as a deterrent: About half of those released from prison return there within three years.

Fortunately, it is possible to break this vicious cycle while also increasing public safety. The most effective way to deter crime, according to a growing body of research, is to increase the probability of getting caught, rather than the punishment received. That’s because most offenders are not particularly forward-looking, so adding years to an already-long possible prison sentence tends not to change their behavior.

Conventional wisdom has long been that the best way to increase the probability of getting caught is to hire more police officers. But technology — in particular, the use of DNA databases — is now providing options that are cheaper and, in many ways, less invasive.

DNA databases for criminal offenders are now used in every U.S. state and in many other countries. In the U.S., state databases are linked to form a national network called CODIS, which is maintained by the FBI. A separate database contains DNA profiles from unsolved crime scenes. Many people imagine that DNA analysis necessarily involves the exposure of sensitive health information, but this tool simply uses DNA to create an identifying string of numbers — like a high-tech, more accurate fingerprint.

The purpose of these databases is to provide new leads in crimes where law enforcement has not yet found the perpetrator. When DNA from a crime scene is uploaded to CODIS, it is compared with the DNA profiles in the offender database. Any matches are sent to local law enforcement and might lead them to a new suspect in what is otherwise a cold case.

What all of this means is that, once they are added to the DNA database, offenders who might have expected to get away with their crimes are now more likely to get caught. Does this deter them from committing new crimes? And if so, how much does it change their behavior?

In new research with Anne Sofie Tegner Anker and Rasmus Landersø, I studied the effects of DNA databases on criminal behavior in Denmark (which has a similar system to the U.S., but much richer and more available data). The bottom line: Expanding government DNA databases to add more criminal offenders has a big deterrent effect, reducing the number of crimes committed.

How do we know? A natural experiment of sorts occurred in Denmark more than a decade ago. An expansion of the DNA database in 2005 added anyone charged with a serious offense (roughly equivalent to a felony in the U.S.). Those charged just after the expansion took effect were added to the database, but otherwise-similar people charged just before the expansion were not. So whether people were in the database depended on the precise timing of their charge — not on their criminal history or something else they could control.

It was then possible to compare people charged before and after the expansion date, to see if their behavior differed over time.

We found that adding people charged with a felony to Denmark’s DNA database reduced the likelihood of another conviction within the following year by a whopping 42%. The effects were driven by young adults, who also began enrolling in school at higher rates once their DNA was on file. We also found that first-time defendants changed their behavior more than those who had already cycled through the system. This suggests that intervening earlier in people’s criminal careers has bigger benefits.

These results are in line with my previous research showing that adding people convicted of felony offenses to DNA databases in the U.S. deterred crime. But the richer Danish data paint a more detailed picture of this technology’s effects, and also inform current policy discussions in the U.S.

The Supreme Court ruled several years ago that adding people charged with a crime (with or without a conviction) to DNA databases is constitutional, but this is not yet the law in many states. Our findings from Denmark suggest that expanding U.S. state databases to include this group could have big crime-reduction benefits. Adding people convicted of misdemeanors could also be effective, because this would similarly include people earlier in their criminal careers.

Yes, collecting and analyzing people’s DNA is costly in terms of privacy. But so is locking people up. DNA databases can help individuals and society avoid that cost. And many popular law enforcement tools, like cameras on every street corner, record far more information about their targets than DNA databases ever could.

In many ways, DNA databases are far less invasive than widely used alternatives. It makes sense to expand their use in the fight against crime.


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