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Winter/Spring 2008 Vol. 8 No. 1



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Not Picture Perfect

©Joshua Sheldon/The Image Bank/Getty Images

Report Advises Against National Database of Ballistic Images


Firearms are used in about two-thirds of the homicides committed each year in the U.S., and detectives investigating these and other gun crimes often turn to the bullets and cartridge cases a shooter leaves behind. Manufacturing processes leave microscopic marks on guns, which in turn leave "toolmarks" on bullets and cartridge cases during the firing process. These marks are thought to be unique to each gun. A firearms examiner might compare the toolmarks on a crime-scene bullet to those on a bullet test-fired from a suspect's gun, to see whether they match. Computerized imaging can help this process on a far larger scale. For example, an investigator can put images of a bullet or casing into a database and search through large numbers of images from other crime scenes and suspects' guns, to see if any have similar toolmarks.

The National Institute of Justice asked the National Research Council to assess whether a national database should be created to hold the images of toolmarks from all new and imported guns. Whenever a gun is sold, images would be entered into the database. The argument for such a database is that it could help investigators track down where the gun used in a crime was first sold.

The Research Council's report advises against creating such a database, in large part because existing technologies could not effectively sort through the many images involved. Images from millions of guns might be entered each year, and many would have similar toolmarks. Current technologies could not reliably distinguish very fine differences between them, and searches would turn up too many possible "matches" to be useful. And the type of ammunition used in a crime may not be the type used when the gun was originally test-fired -- a difference that could be a significant source of error in generating possible matches.

The report does not assess whether toolmark evidence should be allowed in legal proceedings. However, it does note that the assumption that each gun leaves unique toolmarks has not yet been fully demonstrated scientifically. And it advises against a statement often made by firearms examiners in court -- that a bullet or cartridge casing came from a particular gun "to the exclusion of all other firearms." Such statements of absolute certainty lack a firm statistical basis and fail to account for the element of subjectivity involved in declaring a "match," a determination always made by a person. More studies would be needed to determine the extent to which the toolmarks made by a gun are unique and remain the same over time, despite repeated firings.

Although it advises against creating a national reference database of ballistic images, the report concludes that an existing image database -- limited to evidence associated with crimes -- has strong potential for generating leads in criminal investigation. That database is used by more than 200 state and local law enforcement agencies and is administered by the U.S. Bureau of Alcohol, Tobacco, Firearms, and Explosives. The report suggests more than a dozen possible enhancements to promote more effective use of the current system.

It also recommends further research on an alternative approach, "microstamping." This technique imprints a tiny identifier on bullets or guns -- substituting a known unique marking for the toolmarks left by variations in gun manufacturing and firing. Such markings could be inspected at a crime scene with equipment as simple as a magnifying glass, the report says. But before such a system could be implemented, research is needed on whether microstamped identifiers endure repeated firings, how vulnerable they are to tampering, and how using them would affect costs for manufacturers and consumers.   -- Sara Frueh


Ballistic Imaging. Committee to Assess the Feasibility, Accuracy, and Technical Capability of a National Ballistics Database. Committee on Law and Justice and Committee on National Statistics, Division of Behavioral and Social Sciences and Education, and National Materials Advisory Board, Division on Engineering and Physical Sciences (2008, approx. 386 pp.; ISBN 0-309-11724-0; available from the National Academies Press, tel. 1-800-624-6242; $39.00 plus $4.50 shipping for single copies).

The committee was chaired by John E. Rolph, professor of statistics, Marshall School of Business, University of Southern California. The study was funded by the National Institute of Justice of the U.S. Department of Justice.



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Copyright 2008 by the National Academy of Sciences