The DNA Field Experiment

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Abstract

The study compared traditional crime solving to biological evidence techniques in hundreds of cases where biological evidence was available. When conventional investigative techniques were used, a suspect was identified 12 percent of the time, compared to 31 percent of the cases using DNA evidence. In eight percent of cases built on traditional evidence alone a suspect was arrested, compared to the 16 percent arrest rate in DNA cases. The average added cost for processing a single case with DNA evidence was about $1,397. Each additional arrest—an arrest that would not have occurred without DNA processing—cost $14,169.

Introduction

In the United States, DNA analysis is almost exclusively used to investigate violent criminal incidents. Great Britain, by contrast, has employed DNA forensics in nonviolent criminal investigations on a national scale since 2001. The success of this strategy is one reason the National Institute of Justice launched the DNA Field Experiment in five communities (Orange County and Los Angeles, California; Topeka, Kansas; Denver, Colorado; and Phoenix, Arizona). The DNA Field Experiment evaluates the expansion of DNA evidence collection and testing to the investigation of property crimes.

We report the results of a prospective, randomized study of the cost-effectiveness of DNA in investigating high-volume crimes, including residential burglary, commercial burglary, and theft from automobiles. Biological evidence was collected at up to 500 crime scenes in each site between November 2005 and July 2007, and cases were randomly assigned to the treatment and control groups, producing a roughly equal split of cases within each site. In the treatment group, DNA processing as well as traditional practices were used to investigate the case. In the control group, biological evidence was not initially tested, and case outcomes were due only to traditional investigation.

The study’s main findings are that:

• Property crime cases where DNA evidence is processed have more than twice as many suspects identified, twice as many suspects arrested, and more than twice as many cases accepted for prosecution compared with traditional investigation;
• DNA is at least five times as likely to result in a suspect identification compared with fingerprints;
• Suspects identified by DNA had at least twice as many prior felony arrests and convictions as those identified by traditional investigation;
• Blood evidence results in better case outcomes than other biological evidence, particularly evidence from items that were handled or touched;
• Biological material collected by forensic technicians is no more likely to result in a suspect being identified than biological material collected by patrol officers.

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The nonpartisan Urban Institute publishes studies, reports, and books on timely topics worthy of public consideration. The views expressed are those of the authors and should not be attributed to the Urban Institute, its trustees, or its funders.

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