Class versus individual evidence
Class versus individual evidence (Forensic Science)
Class evidence makes up the vast majority of all evidence in forensic cases. For example, a glass fragment can be analyzed to determine its refractive index and chemical makeup. The resultant laboratory report can tell investigators that the fragment’s properties are consistent with a certain type of glass, such as that from windowpanes or car headlights. What the analysis usually cannot reveal is from which particular window or which particular car headlight the fragment comes.
By contrast, individual evidence can be linked to specific objects, such as fingerprints, no two of which have ever been found to be exactly alike. For this reason, any fingerprint that is found must have been made by one, and only one, person. Other examples of individual evidence include human lip prints, ear prints, and sole prints. Researchers have also found through X-ray analyses of skulls that sinus prints—the unique patterns of bone and space in sinus cavities—are also individual. Forensic anthropologists can use this information to identify bodies of long-dead people. Surprisingly, DNA (deoxyribonucleic acid) evidence is not individual, as identical twins have identical DNA.
Many objects that would otherwise fall under the heading of class evidence pick up individual characteristics. For example, the soles of all shoes of a specific model and size come out of their factories looking exactly the same. After they have undergone some substantial...
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Further Reading (Forensic Science)
Beavan, Colin. Fingerprints: The Origins of Crime Detection and the Murder Case That Launched Forensic Science. New York: Hyperion, 2001.
Platt, Richard. Crime Scene: The Ultimate Guide to Forensic Science. New York: Dorling Kindersley, 2003.
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