“Wherever he steps, whatever he touches, whatever he leaves, even unconsciously, will serve as silent evidence against him. Not only his fingerprints or his footprints, but his hair, the fibers from his clothes, the glass he breaks, the tool mark he leaves, the paint he scratches, the blood or semen that he deposits or collects – all these and more bear mute witness against him. This is evidence that does not forget. It is not confused by the excitement of the moment. It is not absent because human witnesses are. It is factual evidence. Physical evidence cannot be wrong; it cannot perjure itself; it cannot be wholly absent. Only its interpretation can err. Only human failure to find it, study and understand it, can diminish its value.”
— Paul L. Kirk, PhD
“Father of Criminalistics”
Crime Investigation: Physical Evidence and the Police
Laboratory Interscience Publishers, Inc., New York, NY 1953 Chapter 1, page 4.
Test firing of a weapon in the Firearms
Section of a forensic lab.
Scope of Work
Criminalists analyze, compare, identify, and interpret physical evidence, then report results for use in the justice system. Forensic laboratories have two primary functions: (1) identifying evidence; and, (2) linking individuals, objects, and locations through physical evidence. The main role of the criminalist is to objectively apply standard, scientific processing techniques of the physical and natural sciences to examine physical evidence. Physical evidence may be anything. It may be as subtle as a whiff of a flammable gas at an arson scene or as obvious as a pool of blood at a homicide scene. The enormous range of material challenges the ingenuity of the criminalist who examines and identifies hair, fibers, blood, seminal and other body fluid stains, drugs, paint, glass, botanicals, soil, flammables and safe insulating material; restores obliterated, smeared or smudged markings; and identifies firearms and compares fired bullets, tool markings, and footwear impressions. In most cases, the amount of the evidence to be tested is very small, such as a drop of blood, a hair, or a piece of glass, but can be a vehicle or other large object.
45 caliber pistol
Crime scene vehicle
Using specialized training, analytical skill, and practical experience, the criminalist separates evidence from items having little or no value. Next, the criminalist sorts, compares, and identifies the evidence, using chemical tests and instruments to develop useful information for investigation or at trial. The criminalist may find, for example, that a bullet has been fired from a particular gun, the DNA profile from a bloodstain inside a suspect’s car is the same as the victim’s DNA profile, or that a fragment of paint from the scene of a hit-and-run accident has come from a particular car. These types of analyses are rarely routine; they require an eye for detail, a broad practical scientific background, and the ability to apply these skills in the laboratory.
Gas chromatograph/mass spectrometer
Perhaps the most important task of the criminalist lies in interpreting the results of the tests to help determine the facts. The results may help to determine the circumstances at the time a crime occurred or to provide details supporting a witness’s statement. Reconstructing the events of a crime can be very difficult. It requires an understanding of the meaning of results from the analysis of physical evidence, of the physical laws and processes involved, and the recognition of how they interact. Finally, any results and conclusions made by the criminalist must be conveyed to the others in the criminal justice system, such as officers, attorneys, and jurors. This is done by written reports and expert testimony. The criminalist must express conclusions so that technical details are understood by the non-scientist jury, attorneys, and judges.
Tire from suspect vehicle
Tire imprint on vehicle roof
Criminalists must be able to think critically and use scientifically valid methods to analyze anything and everything submitted to the laboratory. They must be familiar with many different types of equipment and techniques in order to conduct the necessary testing. They must know basic chemistry concepts as well as have advanced knowledge of instrumental techniques that include polarized light microscopy (PLM), gas chromatography/mass spectroscopy (GC/MS), Fourier Transform Infrared Spectroscopy (FTIR), Raman IR, and scanning electron microscopy (SEM) to name a very few.
Education and Training
The minimum educational requirement for a criminalist is a bachelor’s degree in chemistry, biology, physics, molecular biology, forensic science, or a related physical science. For some positions, a master’s degree is required. Many colleges and universities offer degrees and courses in forensic science. When choosing a forensic science program, it is important to determine whether the program is accredited by the Forensic Science Education Programs Accreditation Commission (FEPAC). (www.fepac-edu.org). Accredited programs offer the necessary amount of science and math required to be a criminalist.
In deciding whether to get a degree in chemistry, biology, or forensic science, study the courses offered. At least 24 semester hours of either chemistry or biology is required and math is a must. Knowledge of statistics is becoming increasingly important. The title of the degree is not as important as the courses taken.
The education of a criminalist never stops. Because forensic science is an ever-evolving field, criminalists must continually increase their knowledge in their discipline. To keep up with the many advances in science, the criminalist must take continuing education courses. After successfully completing an examination, the criminalist may become certified by the American Board of Criminalistics (www.criminalistics.com) in a variety of specialties. Entire forensic laboratories may prove their competence by becoming accredited to the International Organization for Standardization (ISO) standards. ISO accreditation demonstrates best management practices coupled with the best science practices with the competency of the scientific staff. Currently, there are four U.S. accrediting bodies recognized by the International Laboratory Accreditation Cooperation (ILAC) that provide ISO forensic accreditation. Forensic laboratory accreditation is required by law in a number of states.
Scientist preparing swabs for DNA testing.
Scientist examining a sheet for biological and trace evidence.
Criminalistics is a diverse profession and criminalists usually specialize in one or more of the many sub-disciplines, such as firearms and toolmark identification, biology/DNA, controlled substance analysis, or fire and explosion debris analysis. Criminalists work in forensic laboratories in police departments, sheriff offices, district attorney offices, regional and state agencies, medical examiners’ offices, private companies, colleges and universities; and for federal agencies such as the Drug Enforcement Administration (DEA); Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF); Federal Bureau of Investigation (FBI); United States Postal Service; the military forces, and the United States Fish and Wildlife Services. Criminalists assist the United States Department of Justice in helping other countries create or update forensic science services.
The criminalist may start as a “bench” scientist after graduating from college and, through education and dedication, work up to forensic laboratory director. There are many opportunities to teach at community colleges and universities training future criminalists. As forensic science advances, more criminalists will be needed to perform new tests in an ever-expanding field of evidence.
A criminalist specializing in DNA must have a solid scientific foundation and be flexible and willing to routinely implement newly-validated testing reagents, customized laboratory consumables, enhanced automation and instrumentation methods, and new DNA genetic markers. Interpretation of DNA evidence is one of the most challenging aspects of forensic DNA analysis especially as it relates to statistical calculations for DNA profile rarity and new software programs are constantly improving this task. Forensic DNA analysis continues to evolve into new technologies, including Rapid-DNA where forensic DNA results are obtained within about an hour. DNA analysis may be conducted in government and private DNA laboratories, criminal booking agencies, mass disaster sites, and international areas of conflict. Another progressive technology is Next Generation Sequencing (NGS) in which massive amounts of genetic information are obtained through the rapid synthesis of target DNA achieving greater statistical reporting power. DNA testing will always be evolving for the criminalist who chooses DNA as a forensic profession.
Drug chemistry is one of the many forensic disciplines in a typical forensic laboratory. The drug chemist uses a wide variety of techniques and methods including color and microcrystal tests, chromatography (thin layer, gas, liquid, and high-pressure liquid), spectrophotometry (ultraviolet, visible, infrared, raman), spectrometry (mass spectrometry), X-ray spectroscopy (X-ray diffraction), and nuclear magnetic resonance spectroscopy. Many of these tests are considered preliminary in nature as they do not identify a specific compound but a general class of compounds. Techniques that are considered confirmatory are those which actually determine the structure of a compound and thus identify a specific compound instead of a class of compounds. The most common confirmatory instruments are infrared (FTIR), mass spectrometry (MS), nuclear magnetic resonance (NMR), and X-ray diffraction (XRD). The drug chemist may have large quantities of drug materials to analyze or just milligrams of a material. The drugs may be pure or mixed with other substances which then require the chemist to extract the drugs for analysis. Drug analysis normally has the highest number of analyses in forensic laboratories due to the high incidence of drug abuse around the world.
In fire debris analysis, it is necessary to know how flammable liquids are made and how they burn in order to recognize both the flammable liquids and their breakdown products (i.e., combustion products) that may be found in the fire debris.
This cabin exploded because of a leak in a poorly installed propane gas line. Accumulated gas was set off by a loose electrical connection at the furnace. Criminalists often combine multiple skills or work with other disciplines. Determining the cause of the explosion that destroyed this log cabin required collaboration among chemists, metallurgists, and engineers.
Fire investigation was once practiced largely by non-scientists using “rules of thumb.” New research into the production of fire patterns has revealed that much of what the profession thought it “knew” about fire behavior was not accurate. Determining the origin (where the fire started) is not as easy as it was once thought. Several high-profile cases of wrongful conviction have made it clear that there is a need for more scientists with knowledge of chemistry and physics to enter the field. (www.nij.gov/events/nij_conference/2010/Pages/willingham-summary.aspx)
Trace evidence testing covers a wide area of materials to be analyzed such as explosives, gunshot residue, hairs, and fibers. In many cases, criminalists must understand the physics of how evidence is produced.
Criminalists must not only understand the composition of trace evidence but also understand the dynamics that create or alter physical evidence. For example when an explosion occurs, it is very rare that the explosive or device that explodes is completely consumed or destroyed. Rather, they are transformed into residues and very small pieces. It is up to the criminalist to analyze these residues and recognize these small pieces for what they are (i.e., explosive device components) and how they relate back to the original explosion.
Wildlife Forensic Science
Poaching violations, the development of state and federal hunting regulations, the Endangered Species Act of 1973, and the United Nations Convention on International Trade in Endangered Species (CITIES) are some of the factors which helped create this new field.
The major difference between criminal forensic science and wildlife forensic science is that the victim (and occasionally the suspect) is an animal.
The identification of wildlife evidence can be complicated because wildlife enforcement officers rarely seize whole animals which can be readily identified by a museum or zoo expert. More typically parts or the products created from wildlife will be recovered as evidence. The characteristics which define an animal species are rarely present in those parts or products.
Wildlife forensic scientists are often required to develop new ways to identify species through research with carefully documented known specimens before they can examine evidence in a case and testify in court. An additional complication is that, while human forensics deals with only a single species (homo sapiens), wildlife forensic scientists must be prepared to identify evidence from any species in the world that is illegally killed, smuggled, poached, or sold through an illicit market. Examples of wildlife evidence items might be blood on an illegal hunter’s clothing; fresh, frozen, or smoked meats; loose hair; fur coats; reptile leather products, such as purses, belts, and shoes; loose feathers and down; carved ivory objects; sea turtle oil (suntan lotion); shell jewelry; and powdered rhinoceros horn. While it might seem that wildlife forensic scientists face an overwhelming task in developing new and reliable ID techniques, they do have one advantage over other forensic scientists: sample size is rarely a problem. Example seizures of wildlife evidence have included 20,000 pounds of suspected sea turtle meat, 10,000 pounds of ivory, and 300,000 suspected rhinoceros horn pills.
Butler, John M., Forensic DNA series by (Elsevier)
Forensic DNA Typing: Biology, Technology, and Genetics of STR Markers, 2nd Edition, 2005.
Fundamentals of Forensic DNA Typing, 2009.
Advanced Topics in Forensic DNA Typing: Methodology, 2011.
Fisher, Barry A. J. and Fisher, David R., Techniques of Crime Scene Investigation, 8th Edition, CRC Press, New York, NY, 2012.
Inman, K. and Rudin, N., Principles and Practices of Criminalistics, CRC Press, New York, NY, 2001.
Lentini, J., Scientific Protocols for Fire Investigation, 2nd Edition, CRC Press, Boca Raton, FL, 2012.
Mozayani, A. and Noziglia, C., The Forensic Laboratory Handbook Procedures and Practice, 2nd Edition, CRC Press, New York, NY, 2011.
Saferstein R., Criminalistics: An Introduction to Forensic Science, 11th Edition Prentice Hall, Upper Saddle River, NJ, 2014.
Ubelaker, Douglas H., Forensic Science: Current Issues, Future Directions, John Wiley & Sons LTD, 2013.
AAFS Career Webinar (Criminalistics)