The Bone Collector

remains and analyzing bite-mark evidence.
    Friction ridges: The raised lines of skin on fingers, palms, and the soles of feet, whose patterns are unique to each individual. Prints of friction ridges at crime scenes can be classified as (1) plastic (left in an impressionable substance such as putty); (2) evident (left by skin coated with a foreign substance like dust or blood); (3) latent (left by skin contaminated with bodily secretions such as grease or sweat and largely invisible).
    Gas chromatograph/mass spectrometer (GC-MS): Two instruments used in forensic analysis to identify unknown substances such as drugs and trace evidence. They are often linked together. The gas chromatograph separates components in a substance and transmits them to the mass spectrometer, which definitively identifies each of those components.
    Grid: A common approach to searching for evidence whereby the searcher covers a crime scene back and forth in one direction (say, north–south), then covers the same scene in the perpendicular direction (east–west).
    Gunshot residue (GSR): The material—particularly barium and antimony—deposited on the hands and clothing of a person shooting a firearm. GSR remains on human skin for up to six hours if not removed intentionally by washing or inadvertently by excessive contact when a suspect is arrested and handcuffed (a greater risk if the hands are cuffed behind the back).
    Identification of physical evidence: Determining the category or class of material that an item of evidence falls into. This is distinguishable from “individuation,” whichis a determination of the single source the item came from. For example, a torn piece of paper found at a crime scene can be identified as coated 40-pound stock of the type often used in magazine printing. It can be individuated if the piece exactly fits the missing section of a torn page in a particular issue of a magazine found in a suspect’s possession. Individuation, of course, has far more probative value than does identification.
    Individuation of physical evidence: See “Identification of physical evidence.”
    Lividity: The purplish discoloring of portions of the skin of a deceased owing to the darkening and settling of the blood after death
    Locard’s Exchange Principle: Formulated by Edmond Locard, a French criminalist, this theory holds that there is always an exchange of physical evidence between the perpetrator and the crime scene or the victim, however minute or difficult to detect that evidence might be.
    Mass spectrometer: See “Gas chromatograph.”
    Ninhydrin: A chemical that visualizes latent friction-ridge prints on porous surfaces such as paper, cardboard, and wood.
    Physical evidence (PE): In criminal law, PE refers to items or substances presented at trial to support the assertion by the defendant or the prosecution that a particular proposition is true. Physical evidence comprises inanimate objects, bodily materials, and impressions (such as fingerprints).
    Presumptive blood test: Any of a number of chemical techniques for determining if blood residue is present at a crime scene, even if it is not evident to the eye. Most common are tests using luminol and orthotolidine.
    Scanning electron microscope (SEM): An instrument that fires electrons onto a specimen of evidence to be examined and projects the resulting image on a computer monitor. Magnification of 100,000X is possible with SEMs, compared with about 500X in the case of most optical microscopes. The SEM is often combined with an energy-dispersive X-ray unit (EDX), which can identify the elements in a sample at the same time the technician is viewing it.
    Staging: A perpetrator’s efforts to rearrange, add, or remove evidence from a crime scene to make it appear that thecrime he or she has committed did not occur or was committed by someone else.
    Trace evidence: Bits of tiny, sometimes microscopic, substances such as dust, dirt, cellular material, and fibers.
    Unsub: Unknown subject; that is, an unidentified suspect.
    Vacuum-metal deposition (VMD): The most effective means for visualizing latent friction-ridge prints on smooth surfaces. Gold or zinc evaporated in a vacuum chamber coats the object to be examined with a thin layer of metal, thereby making a print visible.

AUTHOR’S NOTE
    I’m indebted to Peter A. Micheels, author of The Detectives, and E. W. Count, author of Cop Talk, whose books were not only wonderfully helpful in researching this one but great