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DNA (deoxyribonucleic acid), genetic typing for forensic purposes was first introduced for casework in 1985. This new technique enabled forensic laboratories to identify an individual at the molecular level. Because history has shown that many rapists and other felons are repeat offenders, some state and federal jurisdictions have passed legislation enabling the collection of DNA samples from their criminals prior to their release. A DNA profile data bank provides a new investigative tool for law enforcement, because by comparing the DNA profile from semen samples collected from a rape victim or from bloodstains left at a crime scene to DNA records on file, a suspect may be identified in much the same manner as when fingerprint records are searched.
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Standard methods of analytical chemistry are called upon to identify the presence of controlled substances and to quantify these materials. In addition to the analysis of unknown powders, liquids, and vegetative materials, the drug chemist may also identify controlled substances in the form of tablets and capsules. Clandestine laboratories use chemicals to produce illegal substances: the quality and quantity of these reagents may be determined by the drug analyst.
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This subspecialty deals with the identification and analysis of unknown chemical substances, accelerants, gun powder residue, explosives and other chemical products. Comparisons are made among known and unknown materials and, often, attempts are made to trace unknown substances to a specific origin.
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The trace analyst combines the methodologies of microscopic, instrumental and chemical techniques in the examination of hair, fibers, glass, soil, plant material, minerals and other substances present in small quantities or size. While it is difficult to make absolute individualizations in these areas (see "Individualization" below), the trace analyst can make identifications with a high degree of certainty and can often establish with confidence partial individuality of a specimen.
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The examination of firearms, discharged bullets, cartridge cases, shotgun shells and other ammunition and various weapons are all conducted by the firearms examiner. Generally, the examiner tries to answer three questions: (1) What kind of ammunition was used? (2) What kind of weapon fired the bullet? (3) Did this gun fire this bullet or cartridge case? Garments and other objects are also examined to detect firearm discharge residue and to determine the distance between the target and the weapon when it was fired. Many firearms examiners also perform tool mark comparisons. With increasing frequency, tools of many kinds are used as weapons or in the perpetuation of crimes. Whenever a tool has been used to move an object, to scratch or injure a surface or to make an impression on an object, it may be possible to identify the tool.
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Latent fingerprint examiners are responsible for processing fingerprints at the crime scene or on the evidence submitted to the forensic science laboratory. There are many chemical and physical methods available to detect and visualize such prints, and upon completion of these steps, the examiner compares the results with known fingerprints submitted from the suspect, victim or other individuals involved in the case. An absolute identification can be based on these comparisons.
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In cases involving tape-recorded messages containing personal threats, false alarms, bomb threats or other criminal violations, it may be necessary to employ the skills of a voiceprint and then compared.
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Forensic serologists apply the principles and techniques of biochemistry, serology, immunology, hematology and molecular biology to the identification and individualization of blood and other body fluids. The questions which are generally answered by the examination are: (1) What type of stain is it? (2) What species does the stain belong to? (3) Does the questioned stain have the same blood groups and isoenzymes or DNA patterns as a certain known sample? (4) Can serological reconstruction be used to help individualize the sample in terms of origin?
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Criminalists who specialize in impression evidence are concerned with various types of two-or-three dimensional markings such as footwear impressions, tire impressions and footprints. Evidence impression marks are compared with known markings made by the object suspected of causing the imprint or impression. Some types of impression evidence such as fingerprints and tool marks fall within the province of other subspecialties discussed above.
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Such an examination played a major role in our consideration of the two cases involving children: the Lindbergh baby and Jon Benet Ramsey. The questioned document examiner is involved in the scientific examination of handwriting, typewriting, printing, photocopying or other mechanical production of written material. This specialist may also analyze the ink, paper and other components of documents such as wills, letters and ransom notes. Other examinations include identifying the source or write of the document, deciphering obliterated or erased writing, detecting alterations and examining indented writing and burned or charred documents.
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Historically, it has been customary to designate the crime scene as the area where a criminal act has taken place. Actually, the crime scene may comprise more than one site. In the macroscopic sense, crime scenes could also refer to areas other than physical locations. For example, the victim's body, the suspect's body, or any part of a vehicle used in connection with the crime are considered crime scenes. In addition, other locations or persons involved in the crime are regarded as continuations of the crime scene(s).
In the microscopic sense, any piece of physical material related to the crime is also deemed a crime scene, such as a cigarette butt or the scrapings of a victim's fingernails. Each case, therefore, may contain many of these microscopic and macroscopic crime scenes and each could yield information useful to the solution of the crime.
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Physical anthropology is the science pertaining to the human skeleton and how it has developed and evolved throughout the history of the human race. Forensic anthropologists are physical anthropologists who specialize in recovering and examining human skeletal remains where legal questions are involved. The examination of recovered bones can reveal whether they are human; the type of injury, if any, to the bones; the approximate age, height and stature of the person; his/her sex; and information about medical conditions and any childbearing history. These experts can also ascertain whether the skeletal remains were deposited recently or whether they belong to people who died many decades or even centuries ago.
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Entomology is the study of the life cycles of insects. After an organism dies, various insects lay their eggs on the exposed surfaces of the body. The behavior of these insects is predictable, and the waves of insect infestation of a human body follow certain known patterns and time intervals. Forensic entomologists use this information to estimate the time since death in human remains that have not been discovered or protected for some days after death. New developments in DNA typing of maggots and insects help in this regard.
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Those who are trained specialists in photographic documentation of crime scenes, accident scenes, and physical evidence are forensic photographers. Often associated with crime scene investigation teams or with full-service forensic science laboratories, these photographers are involved in photograph enhancement, specialized photography utilizing alternate light sources, photographic and video conversion or enhancement and image processing and enhancement.
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Crime scene reconstruction is the process of determining the sequence of events, criminal activities, and logical predictions about what occurred during and after the crime. Crime scenes are generally reconstructed through study of the crime scene patterns, application of logic, and the examination of physical evidence. Reconstruction not only involves the scientific analysis of a scene, interpretation of scene pattern evidence and laboratory examination of physical evidence, but also involves a systematic study of related information and the formulation of a logical theory. Often, it is extremely important to determine the actual sequence of events of a crime, to verify statements, to limit the possibilities of alibis, and to develop investigative leads. The need to conduct a scene reconstruction is one major reason for maintaining the integrity of a crime scene. If the scene was altered during processing, this will sometimes seriously affect the ability to perform reconstruction.
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Unit objectives are to: Investigate crime related to computer systems and electronic data; Provide technical investigative and forensic assistance to other agencies; Examine and analyze electronic evidence; Increase awareness of Internet safety issues in the community, targeting the most vulnerable groups of potential victims - children, parents and senior citizens; Train other law enforcement, prosecutorial and judicial personnel in appropriate methods of search and seizure of computer systems and electronic evidence, and; Conduct covert investigations.
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