Criminalistics is the science and profession dealing with the recognition, collection, identification, individualization, and interpretation of physical evidence, and the application of the natural sciences to law-science matters. It is not possible for a single person to become proficient in the examination and analysis of all types of physical evidence. Increasingly, criminalists and other workers in forensic science laboratories are specializing in the examination of one or a few types of physical evidence. For example, forensic biologists analyze the biological or genetic properties of evidence, trace evidence analysts identify material that is transferred between two objects and determine its origin, and firearms and toolmark experts examine firearms, ammunition components, and tools and marks left by them. See also Forensic medicine.
A wide variety of techniques are used by criminalists for the location and collection of evidence at crime scenes as well as for the examination and analysis of that evidence in the laboratory. Crime scene techniques may involve the use of lasers or other light sources to locate biological stains or minute fibers or paint particles, chemical tests for lead around suspected bullet holes, electrostatic devices to recover a dusty shoe sole impression from a floor, or special reagents for the development of latent fingerprints.
Many techniques used in the forensic laboratory are the same ones that are used by analytical chemists, molecular biologists, materials scientists, and so on. Often these techniques are adapted to the special requirements of the forensic science laboratory. Infrared spectroscopy, mass spectrometry, gas chromatography, optical and electron microscopy, and a host of other standard analytical chemistry techniques find common use by criminalists.
Routine techniques and procedures have been developed by forensic scientists which have little or no application outside the forensic laboratory. Examples are the determination of genetic markers in minute fragments of dried biological material, the determination of the refractive index of microscopic glass fragments, the microscopic comparison of individual human hairs, and the microscopic comparison of markings on the surface of bullets.
