According to one definition, the word “forensic” means the application of scientific knowledge to legal problems. The term “forensic science” refers to a group of scientific disciplines which are concerned with the application of their particular scientific area of expertise to law enforcement, criminal, civil, legal, and judicial matters. It is beyond the scope of this article to provide detailed descriptions of the various forensic science disciplines so the reader is therefore referred to the many excellent textbooks and reviews of the forensic sciences for more detailed descriptions. This article provides only a very broad overview of the disciplines, with an emphasis on how forensic pathologists might interact with each. Where possible, a specific organization within each discipline, that is the recognized certifying agency for that profession is provided. Readers should beware that there are other organizations and/or “boards” that present themselves as legitimate. Such entities may or may not be reputable.


Before providing a short description of the forensic disciplines, it is necessary to discuss three concepts that are important in all forensic sciences.

Chain of Custody

The first involves maintaining the proper “chain of custody” when dealing with evidence. Evidence of whatever type must be carefully and properly documented and evaluated. Because of the nature of certain types of evidence it cannot all be collected and preserved indefinitely. An example is a human corpse that is evaluated at autopsy. In such instances, proper documentation is essential in order to re-evaluate the evidence (the body) at a later date. In the case of an autopsy, such documentation is performed via diagrams, photographs, and an autopsy report. There are many other types of evidence that also require collection and preservation; for example, trace evidence such as hairs or fibers discovered at a crime scene. Some forms of evidence are actually consumed or destroyed during evaluation (for example, blood samples being tested for drugs).

Maintaining a proper “chain of custody” involves producing and maintaining written documentation which accompanies the evidence and provides an uninterrupted timeline showing the secure location of the evidence from the time that it was dis-covered until the present time. Any transfer of evidence from one person or secure location to another must be documented. Maintaining this chain of custody helps to ensure that the evidence has not been contaminated or compromised in any way. If the proper “chain of custody” is not maintained, the breaking of the chain may well provide a potential reason for such evidence to be inadmissible in court.



Admissibility of Tests, Evidence and Testimony

The second issue of concern that crosses all fields of forensic science involves the existence of legal standards for the admissibility of forensic tests and expert testimony. One legal standard for the admissibility of a forensic test is Frye v United States, which states that the forensic technique in question must have “general acceptance” by the scientific community. Rule 702 of the Federal Rules of Evidence regulates the admissibility of expert testimony in regard to a test or discipline. Daubert v Merrell Dow Pharmaceutical, Inc states that the decision about the admissibility of scientific evidence resides with the judge hearing the case.

Expert Witness

The third issue that relates to all forensic science disciplines is the concept of the expert witness. In contrast to a “fact witness,” who is usually only able to relate the facts of the issue at hand as he/she observed them, an “expert witness,” because of his/her specific expertise within a particular discipline, is also able to offer opin-ions regarding issues that relate to the specific discipline. In order to be recognized as an expert witness, the witness must be officially qualified, or recognized as an expert, by the court. Usually this involves a legal process referred to as voir dire,

wherein the credentials, training, experience, etc. are presented to the court via questions/answers between an attorney and the witness. So long as this presenta-tion is acceptable to both sides and the judge, a witness may be qualified to testify as an expert in a particular field.


Forensic Science Disciplines

Forensic Pathology

Forensic pathology represents a subspecialty within the medical specialty of pathol-ogy (see discussion of pathology in Chapter 1), dealing specifically with the investigation of sudden, unexpected, and/or violent deaths. The autopsy is central to the practice of forensic pathology.

Forensic Anthropology

Forensic anthropology is a subspecialty within the scientific field of physical anthro-pology (the study of human beings in relation to their physical character), in which forensic anthropologists examine skeletal remains (bones). Forensic anthropologists attempt to answer questions about bones, including questions regarding species of origin (human versus nonhuman), gender, age, race, stature, nutritional status, exis-tence of disease processes, and the presence and character of skeletal trauma. A forensic pathologist may consult with a forensic anthropologist when attempting to address any of the questions above. A frequent instance of consultation occurs when the forensic pathologist is presented with a badly decomposed or skeletonized corpse that is unidentified.

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Forensic Odontology

Forensic odontology is a subspecialty within dentistry in which a dentist has spe-cialized expertise in using dental examination to assist in the identification of human remains, and in the evaluation of bite-marks, wherein a bite-mark on a victim may be “matched” to a suspect . The majority of a forensic odontologist’s involvement in forensic casework involves assisting forensic pathol-ogists in the identification of bodies. Assistance is usually provided in cases where the body is not visibly identifiable, and identification by fingerprint comparison or other means is not possible. The most common types of cases are persons who are badly burned and those who are badly decomposed

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Forensic Entomology

Forensic entomology is a subspecialty within the biological science discipline of entomology (the study of insects) that primarily deals with insect succession pat-terns in decomposing human bodies. Evaluation of insects (including larval stages, In certain circumstances, information regarding the location of death may also be ascertained. Forensic pathologists do not consult with foren-sic entomologists in all decomposed cases, but will consult with them on select cases where estimating the time of death may be very important (for example, in homicides with decomposition and insect activity).

Forensic Toxicology

Forensic toxicology is a discipline that involves the identification and quantification of drugs and other poisons or toxins in body tissues, including blood. “Screening tests” are said to be “qualitative,” where a test is either positive (indicating that the drug/toxin is present) or negative (indicating that the drug/toxin is not present). When specific levels of drugs or toxins are determined, the tests are said to be “quantitative.” For a result to have forensic significance, two separate method-ologies are required, an initial (screening) test, and a confirmatory (quantitative) test. Another function of some toxicology laboratories is drug identification. For example, if a bag of white powdery substance is found in the pocket of a dead per-son, the substance can be submitted to the laboratory for identification. Forensic pathologists rely a great deal on the forensic toxicology laboratory. In many juris-dictions, toxicology testing is performed on a majority of the autopsy cases. In a significant percentage of forensic autopsy cases, the cause of death is related to the toxicology results. Forensic toxicology laboratories should be appropriately accredited by an officially recognized agency, such as the American Board of Forensic Toxicology. Toxicologists may have varying levels of education. Board certification in forensic toxicology is conferred by the American Board of Forensic Toxicology.

Forensic Psychiatry

Forensic psychiatry represents a discipline dealing with the evaluation of the men-tal state of criminals. Occasionally, forensic pathologists will interact with forensic psychiatrists and police investigators to form a “psychiatric profile” of a suspect in a particular murder or series of murders. A “psychological autopsy” is sometimes necessary when attempting to determine the state of mind of a suicide victim. Board certification in forensic psychiatry is available via the American Board of Psychiatry and Neurology.


Trace Evidence

Trace evidence is a general term used to describe various relatively small pieces of evidence that can be evaluated scientifically. Such evidence can include such items as hair, fiber components, gunpowder, etc.), accelerants, and explosives. With certain types of evidence, the mere identification of the trace evidence may have significance in a particular case, for example, the identification of gunpow-der on the clothing of a shooting victim. With other types of trace evidence, crime laboratory scientists may be able to “match” or “associate” a particular piece of evi-dence collected from a crime scene to a source, including the alleged perpetrator

Fig. 2.6 Microscopic comparison of a strand of evidence hair, compared with a hair standard obtained from a suspect of a crime. For example, a paint chip collected from the clothing of a hit-and-run pedestrian victim may be matched to a specific vehicle. Forensic pathologist interaction with trace evidence analysts is usually via the recognition and collection of pertinent trace evidence on a body by the forensic pathologist with subsequent submission of the evidence to the crime laboratory. Trace evidence evaluations typically occur within the larger setting of a crime laboratory. Crime laboratories must be accredited by the American Society of Crime Laboratory Directors (ASCLD). Trace evidence analysts can be certified via the American Board of Criminalistics (ABC).

Firearms and Toolmarks Examiners

Firearms and toolmarks examiners are forensic scientists with a specific expertise in the evaluation of firearms and ammunition. As part of their job, these scientists are able to match an evidence bullet (such as that collected from a body at autopsy) to a particular suspect weapon. The first step in attempting to determine whether or not a suspect weapon fired an evidence bullet is to determine the “class characteristics” of each. In regard to firearms having a rifled barrel (rifles and most handguns), the class characteristics include the caliber (diameter) of the barrel (and bullet), the number of lands and grooves (alternating raised and lowered areas within the inner surface of the barrel that spiral along the course of the barrel) of the barrel and imprinted on the sides of the bullet, and the direction of the spiraling (the “twist”) within the barrel and imprinted on the sides of the bullet. If an evidence bullet has different class characteristics than a particular suspect weapon, the weapon can be excluded as the one that fired the bullet.


A deformed bullet collected at autopsy. Note the land and groove impression marks on the sides of the bullet

If the class characteristics are the same, then the firearms examiner has to make a more precise comparison. One way of doing this is to have the examiner fire a bullet from the suspect weapon (often into a watertank). The examiner then collects the bullet (the exemplar) and compares the exemplar to the evidence bullet, using a “comparison microscope” . Besides cre-ating marks that correspond to the lands and grooves of the barrel, rifled firearms produce unique, weapon-specific, microscopic marks (“striations”) on the sides of bullets as the bullets travel through the barrel. These marks are created by the phys-ical machine-produced make-up of the inside of the barrel. They are unique to an individual weapon (no two weapons are identical), and they produce essentially

identical microscopic markings on every bullet fired from the same weapon. By comparing these “toolmarks” that are inscribed by the inside of the barrel on the sides of the exemplar bullet to those present on the evidence bullet, an examiner can determine if the evidence bullet was fired from the suspect weapon . An evidence bullet compared to a standard bullet fired from a suspect weapon. By aligning the striations, an evidence bullet can be matched to a specific weapon

Other toolmark patterns can allow examiners to “match” bullet casings to specific weapons (firing pin impressions, ejector marks, extractor marks, etc.). Marks left by other items, such as knife blades or blunt instruments, may also be specific enough to allow toolmarks examiners to match a suspect weapon to a crime scene or even occa-sionally to a body (via marks produced in cartilage or bone). Firearms and toolmarks examiners are also able to evaluate firearms regarding functionality, answering questions related to whether or not a firearm functions appropriately, etc. Forensic pathologists frequently collect and submit evidence from bodies for firearms and toolmarks examination, mostly in the form of firearm projectiles recovered during autopsy. The official certifying organization within this forensic discipline is the Association of Firearm and Tool Mark Examiners (AFTE).


Document Examination

Document examiners evaluate handwriting or machine-produced printing (typewriters, computer printer, copiers, etc.) and other documents. As such, these forensic scientists play a very important role in a variety of crimes, including forgeries, fraud cases, and counterfeit operations. Most interaction with forensic pathologists occurs in suicide cases, where document examiners can compare suicide notes with exemplars of the suicide victim’s known handwriting to establish whether or not the victim actually wrote the suicide note (Disc Image 2.5). Document examiners occasionally perform other forensic tests, such as fingerprint analysis, impression analysis, or voice analysis. Board certification within this forensic discipline is available through the American Board of Forensic Document Examiners (ABFDE).

Fingerprint Evidence

Ever since fingerprints were discovered as a valuable means for identifying peo-ple, the discipline has been an important part of police and forensic investigations. Fingerprints represent unique patterns of the ridges on the pads of the fingers (including the thumbs). The ridges occur in the epidermis (the part of the skin closest to the surface) but extend into the dermis (the deeper part of the skin). Barring changes related to scar formation, which can obliterate portions of a finger-print, fingerprints remain the same throughout an individual’s life. The presumption, which has essentially been proven by decades of experience and casework, is that each individual has their own unique set of fingerprints. No two fingerprints have ever been found to be exactly identical even between identical twins. Therefore, a fingerprint represents a specific, individual characteristic of a particular per-son. Fingerprint examiners rely on various class characteristics (loops, whorls, and arches) as well as individual characteristics (“ridge characteristics” or “minutiae”) of fingerprints in their examinations. An evidence fingerprint (such as a “latent” or invisible fingerprint) at a crime scene can be matched to a known print in a database. A variety of methods are used to collect and preserve evidence fingerprints. Several automated fingerprint identification systems (AFIS) are available: these are com-puterized databases of fingerprints that are on-file within various law enforcement agencies. For forensic pathologists, fingerprint comparison can be extremely useful in identifying an unknown corpse. In many offices, it is a standard operating proce-dure to create a fingerprint record of all bodies. Certification of fingerprint analysts can be obtained via the International Association for Identification.


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