homicide, suicide, or accident occurred and will certify the cause and manner of death.

Crime scene evidence moves through a chain of custody in which, depending on their physical characteristics (e.g., blood, fiber, handwriting), samples are analyzed according to any of a number of analytical protocols, and results are reported to law enforcement and court officials. When evidence is analyzed, typically forensic science “attempts to uncover the actions or happenings of an event … by way of (1) identification (categorization), (2) individualization, (3) association, and (4) reconstruction.”1 Evidence also is analyzed for the purpose of excluding individuals or sources.

Not all forensic services are performed in traditional crime laboratories by trained forensic scientists. Some forensic tests might be conducted by a sworn law enforcement officer with no scientific training or credentials, other than experience. In smaller jurisdictions, members of the local police or sheriff’s department might conduct the analyses of evidence, such as latent print examinations and footwear comparisons. In the United States, if evidence is sent to a crime laboratory, that facility might be publicly or privately operated, although private laboratories typically do not visit crime scenes to collect evidence or serve as the first recipient of physical evidence. Public crime laboratories are organized at the city, county, state, or federal level. A law enforcement agency that does not operate its own crime laboratory typically has access to a higher-level laboratory (e.g., at the state or county level) or a private laboratory for analysis of evidence.

According to a 2005 census by the Bureau of Justice Statistics (BJS),2 389 publicly funded forensic crime laboratories were operating in the United States in 2005: These included 210 state or regional laboratories, 84 county laboratories, 62 municipal laboratories, and 33 federal laboratories, and they received evidence from nearly 2.7 million criminal cases3 in 2005. These laboratories are staffed by individuals with a wide range of training and expertise, from scientists with Ph.D.s to technicians who have been trained largely on the job. No data are available on the size and depth of the private forensic laboratories, except for private DNA laboratories.

In general, a traditional crime laboratory has been defined as constituting “a single laboratory or system comprised of scientists analyzing evidence


K. Inman and N. Rudin. 2002. The origin of evidence. Forensic Science International 126:11-16.


M.R. Durose. 2008. Census of Publicly Funded Forensic Crime Laboratories, 2005. U.S. Department of Justice, Office of Justice Programs, Bureau of Justice Statistics. Available at www.ojp.usdoj.gov/bjs/pub/pdf/cpffcl05.pdf.


Ibid., p. 9. “A ‘case’ is defined as evidence submitted from a single criminal investigation. A case may include multiple ‘requests’ for forensic services. For example, one case may include a request for biology screening and a request for latent prints.”

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