Criminalistics in the Forensic Sciences
In its broadest sense, forensic science is defined as the application of the sciences as it pertains to legal matters or problems. These matters may be involved with criminal laws, such as a case involving a perpetrator accused of murder; with civil laws, such as a case involving the determination of liability in an industrial accident; or with governmental regulations, such as the random drug testing of government employees. Several specialties, or disciplines, can be found within the forensic sciences. These include areas such as medicine/pathology, criminalistics,engineering, odontology, entomology, anthropology and many others. Though the terms ‘criminalistics’ and ‘forensic science’ may have different meanings in different parts of the world, the information presented will consider criminalistics as a discipline within the forensic sciences.
In the United States, criminalistics is the broadest subdivision found in the forensic sciences. Criminalistics, which is best defined by the California Association of Criminalists (CAC), is the profession and scientific discipline directed toward the recognition, identification, individualization and evaluation of physical evidence by application of the natural sciences to law-science matters. A criminalist uses the scientific principle of chemistry, biology and physics to elicit information from crime scenes and physical evidence. Through the application of the scientific method using these natural sciences, the evaluation of evidence can be accomplished in a clear, unbiased and accurate manner. Adherence to the scientific method directs the forensic scientist to advocate the truth on behalf of the evidence, not for a particular side.
History of Criminalistics
The history of criminalistics does not have a single person to credit for its inception. In fact, much of the technology in criminalistics is borrowed from other sciences and applied to legal matters. There were many contributors to the birth of the field through the mid-1800s to the early 1900s. Sir Arthur Conan Doyle’s Sherlock Holmes is often credited as the fictional father of criminalistics, using methods in criminalistics long before the science was recognized and accepted. Mathieu Orfila is credited as the father of forensic toxicology. He is also credited with being the first expert witness in a criminal trial in the 1840s. In the 1880s Alphonse Bertillon created the first classification system attempting to achieve personal indi-vidualization, called anthropometry, and Hans Gross coined the term Kriminalistik. Shortly thereafter, in the 1890s, Francis Galton published his study on fingerprints. Around the 1910s several contributors were added to history: Landsteiner discovered blood groups (i.e. A, B, H); Leone Lattes obtained blood types from dried blood; Calvin Goddard published his work on firearms comparisons; and Albert Osborn undertook document examinations. Then, in 1920, Edmond Locard postulated his ‘exchange principle’, a fundamental contribution to the field upon which many of the specialties in criminalistics are based. Locard’s police laboratory in Lyon, France, was so successful that it gave the needed impetus to the formation of police laboratories and crime laboratories in Europe and the United States. In fact, the first crime laboratories were opening in the late 1920s in the United States. In the 1930s police science and criminalistics were emerging in academia, and in the late 1940s the school of criminology was formed at the University of California at Berkeley, headed by Paul Kirk. As new technology was emerging in the 1960s, England’s Home Office created the Central Research Establishment, the first forensic research center in the world. The 1970s, 1980s and 1990s saw an explosion of information and analytical methods, as the world’s technological advances and instrumentation were (and still are) improving.
Physical Evidence
Physical evidence can be anything, from massive objects as large as a building to submicroscopic molecules of a fleeting vapor. Some say that physical evidence is a silent witness. It can help show that a crime has been committed (corpus delecti) and give insight to the perpetrator’s method of operation ( modus operandi). Physical evidence can provide investigative leads, provide a connection between sus-pect(s) and victim(s), help identify and individualize persons or objects involved, and assist in substantiating or disproving witness statements.
The premise for our work in criminalistics is based on Locard’s exchange principle. It states that whenever two objects come into contact with one another, there is always a transfer of material across the contact boundaries. In the 1950s, Paul Kirk added that no criminal can perpetrate a crime without leaving evidence behind or taking evidence away. Science and technology, therefore, are the limiting factors in the detection of transfers of evidence. The role of the criminalist is to recognize and collect these evidence exchanges at the scene of the crime and, through the rigorous examination of physical evidence in the laboratory, help make the facts of the case clear for an investigator, judge or jury.
An Introduction to the Disciplines in Criminalistics
Criminalistics is unique among the forensic sciences in that it is the only specialty to have a number of seemingly unrelated disciplines within it. This article will take an introductory look at these disciplines, briefly describing the types of evidence encountered and the methods used in each area. For further details regarding each of the disciplines and their examination processes, the reader is referred to the appropriate areas in the topic.
Crime scene processing
Truly, the most challenging and the most important aspects of any physical evidence examination begin at the scene of the crime. The recognition, documentation and collection of physical evidence are crucial steps needed to elicit information from physical evidence. These tasks can be accomplished with the criminalist or crime scene investigator who has special knowledge, skills and abilities. The fundamental tasks involved in any crime scene include securing the crime scene, properly searching and documenting the scene, and recognizing, collecting and packaging physical evidence. Because each crime scene is unique, criminalists need good communication with the investigators and flexibility with the crime scene environment in order to accomplish these tasks in an expedient, yet efficient and competent manner. No amount of work or dedication in the laboratory can ever substitute for a poorly processed crime scene.
Some crime scenes require further knowledge, skills and abilities in particular subject areas in order to provide crime scene reconstructions. These scenes may include clandestine laboratory investigations where illicit and dangerous drugs are manufactured, crime scenes with extensive bloodstain patterns that must be interpreted, arson and explosive crime scenes with their massive and intense destruction, and scenes involving firearm trajectories with several firearms being discharged. Together with the evidence examination results, the criminalist can connect the information and render an opinion regarding the events of the crime.
Forensic photography
Photography is an art known to many, but few recognize that photography in the forensic sciences requires not only the fundamental photographic skills but also the understanding and appreciation of physical evidence and the need to properly document it. Forensic photographers take advantage of the properties of light, special filters and film emulsions available to them to create a permanent record of physical evidence. Many large laboratories have a staff of photographers with the equipment and studio necessary to properly document evidence. For some evidence categories, photography is the only means in which evidence can be collected and preserved.
The forensic photographer may also process the film and provide enlargements for court displays, maintain archive negative files for cases, and provide photographic equipment repair and technical advice. He or she is called out to crime scenes to document evidence when the photographic expertise of the crime scene investigator is limited. Forensic photographers will examine and provide expert testimony in cases where the evidence item is exposed film.
The new technology of imaging is creating exciting changes for the forensic photographer, who may also be working with computerized formats for image capturing in addition to emulsion film. Forensic imaging may soon be the title that replaces forensic photography. For example, the Los Angeles County Sheriff’s Department is converting from obtaining booking photographs on conventional film emulsion to taking them on a computerized, digital format.
Fingerprints
Fingerprint evidence is a very well known evidence category that can individualize evidence to a single person. Fingerprint examiners provide individualiza-tions and eliminations of latent friction ridge prints obtained from objects at the crime scene to known persons. Although the evidence items are routinely fingerprints, they may also include palm, toe or foot prints. During the analysis, the fingerprint examiner compares the class (i.e. the print pattern, such as arch, loop or whorl) and minutiae (i.e. the presence of ridge features within the pattern, such as bifurcations, islands, ridge endings and their spatial relationships) of the objects of interest. Individualization is achieved when a sufficient number of minutiae are present between the comparative prints. Currently, there is some disagreement among the experts as to what constitutes a sufficient number of comparative points. Some argue that a minimum number must always be found, whereas others offer that the number will depend on the minutiae present.
Special methods are available for the development of latent fingerprints, including fingerprint powders, chemical processing and laser or alternative imaging techniques. Larger law enforcement agencies may also have automated fingerprint identification systems (AFIS) that automate fingerprint searches against computer databases. A qualified fingerprint examiner compares the possible candidates selected in the search to determine if an individualization can be made.
Drug analysis
A drug can be defined as a natural or synthetic substance that will affect a physiological or psychological change in the human body. These substances, prior to the introduction into the human body, can be found in many forms, including plant materials, powders, tablets, capsules, liquids and gases. Many drugs are controlled or regulated by laws, which can depend on their medicinal characteristics and their potential for abuse. The drug analysis case load in many laboratories is generally high. Well over 50% of all cases submitted to crime laboratories in the United States involve drug, alcohol or other toxico-logical analysis.
The task of the criminalist is to isolate and identify the unknown substance and determine whether it is a dangerous or illicit drug. The preliminary examination of materials may include visual examination, magnified examination through a stereobinocular microscope, and chemical spot tests, which indicate the presence of a drug type depending on a color change. Confirmation of preliminary results is usually obtained from microcrystalline tests using a polarized light microscope, Fourier transform infrared (FTIR) absorption spectroscopy or gas chromatography with mass spectrometry (GC-MS).
Toxicology and blood alcohol
Toxicology, meaning the ‘study of toxins’ in root form, is closely related to drug analysis. Drug analysis concerns natural or synthetic substances before introduction into the body, whereas toxicology concerns these substances and their metabolites after introduction into the body. Toxicology can, in part, provide investigative information regarding driving-while-impaired cases, contribute to random drug testing of employees and assist pathologists with cause of death determination. Blood alcohol determination, although a part of toxicology, has become such an important analysis in the eyes of society that many laboratories in the United States have separated this analytical area from other toxicological methods.
The task of the toxicologist or blood alcohol analyst is to isolate and identify alcohol (specifically ethanol), illicit and prescription drugs, poisons and other toxins in blood, urine and tissue samples. Alcohol can also be obtained from human breath samples. The analysis determines the qualitative (presence) and quantitative (amount) properties of drugs and toxins in the body. The preliminary examinations may include extraction and purification methods followed by radioimmunoassay (RIA), thin-layer chromatography (TLC) and ultraviolet absorption (UV) spec-troscopy. Modern screening techniques incorporate enzyme immunoassay methods with little or no extraction or purification of the sample. Currently, the application of GC-MS is the standard used for confirmation and quantitation. An evaluation of the results may include expert opinions regarding mental and/or physical impairment of the tested subject while using the detected substances or their metabolites.
Forensic biology
Historically, there has been a distinction between conventional forensic serological methods and de-oxyribonucleic acid (DNA) methods. Conventional serological methods have been limited in the forensic sciences because of the difficulty, or even inability, of many testing procedures to successfully yield results on small, dried stains. Advances in DNA methods can now reliably test smaller and more degraded samples and have replaced many of the conventional serological methods. Today these examinations fall under the generalized heading of forensic biology, and the original task of identification and individualization of body fluids and tissues remains the focus.
The most common samples tested in the laboratory are blood, semen and vaginal fluids. Other body fluids, such as feces, milk, saliva, sweat, tears and urine, and tissues, such as brain, bone, skin and muscle, may also challenge the criminalist in the identification and individualization of persons of interest. The identification process begins with the visual observation of the physical properties, such as color, solubility and taction; chemical color or luminescent tests; ultraviolet (UV) or alternate light source (ALS) fluorescence or dampening; and stereobinocu-lar, brightfield, phase contrast and other microscopical examinations with or without staining techniques. Once confirmation of a body fluid or tissue is made, it is followed by species identification to determine whether the sample is of human or animal origin.
Individualization of a bodily fluid or tissue is performed by a comparison of genetic markers from the evidentiary item with the exemplar reference sample(s). Conventional serological methods include agglutination techniques (e.g. ABO typing) and electrophoretic methods comparing polymorphic enzymes and proteins. Modern DNA methods utilize advances in gene mapping to compare regions of interest of DNA strands. Restriction fragment length polymorphism (RFLP), polymerase chain reaction (PCR), amplified fragment length polymorphism (AmpFLP), mitochondrial DNA (mtDNA) and other methods are used to individualize DNA fragments.
Trace evidence
Trace evidence is a unique discipline in criminalistics, as it has within itself many specialties. Trace evidence is the only discipline in the forensic sciences that includes a wide range of examined materials that are unrelated. The methods and techniques used in trace evidence examinations can be broken down into three evidence categories: patterned evidence, comparative evidence, and physical and chemical properties evidence.
Patterned evidence is the most powerful of the trace evidence categories. It includes the identification and individualization of footwear, tire track, glove, fabric and clothing impressions and physical matches of cut, broken or torn items. During the analysis, the criminalist compares the class and accidental characteristics of the objects of interest. Individualization is achieved when a sufficient number of accidental characteristics are present between the comparative items. The examination of patterned evidence includes visual and stereomicroscopic examinations. First, the criminalist compares the class characteristics, which include the size, shape and design of the manufacturer’s pattern, and, if appropriate, the general wear pattern, on the evidence item with the exemplar. Then the criminalist locates and compares the accidental characteristics, which include the size, shape and spatial relationship of the points of interest. These points may be nicks and gouges on a shoe outsole or tire tread, a jagged edge from a torn item, or any other unique feature. Methods of enhancement may be needed to resolve sufficiently the detail of a patterned impression. For items to be individualized, the evidence items and the exemplars must be examined and compared in their true, life-sized forms; nonlife-sized photographs or other reproductions without a scale are unsuitable for comparison.
Comparative evidence is the next category and includes the identification and the attempt toward individualization of items. The types of evidence encountered by the criminalist include natural and synthetic textile fibers, fabrics and ropes; human and animal hairs; soil samples; and a variety of glass and paint sources. Comparative evidence analysis begins with visual and stereormicroscopic preliminary examinations. Chemical spot tests may also be used in the preliminary examination of paint. Further examination is performed using various types of comparison microscopy (e.g. brightfield, polarized, differential, phase contrast and fluorescent), FTIR, ultraviolet-to-visible range (UV-Vis) spectrophotometry, GC, GC-MS, pyrolysis-GC or GC-MS, TLC, X-ray fluorescence (XRF) and scanning electron microscopy with energy dispersive X-ray (SEM-EDX) microanalysis. Often this type of evidence corroborates or refutes investigative information. It is only under rare circumstances that these types of evidence categories yield an individualization.
Physical and chemical properties evidence involves only the identification or detection of a substance in evidence items. These trace evidence areas include gunshot primer residue (GSR) analysis, mace and pepper spray detection, exploding money-dye pack detection, fire debris analysis, explosives residue analysis and explosive device reconstruction, auto-motive lamp on-off determination, and unknown material identification. The methods of examination are similar to the chemical, microscopic and instrumental methods used in the analysis of comparative evidence.
Toolmarks and firearms
Toolmarks and firearms analysis involves the identification and individualization of indentations and striations on surfaces. Firearms evidence comparisons are a specialized area of toolmark analysis. Toolmark analysis may involve the comparison of screwdrivers and crowbars to window pry marks, and pliers and bolt cutters to cut items such as padlocks and cables. The firearms examination unit routinely compares striations on bullets and bullet jacketing and stria-tions and indentations on cartridge cases to specific firearms. In the absence of a suspect firearm, the examination of these items may provide information regarding the possible types of firearm capable of producing the marks on the items. The comparison begins with the reproduction of the evidence mark with the suspect tool. This is easier for firearms, as the marks are replicated by firing a cartridge in the firearm and recovering the casing and bullet. Toolmarks, on the other hand, can pose a real challenge to the criminalist who is attempting to replicate the exact angle and direction of the tool relative to the surface, as a change in either can alter the characteristics of the indentation or striation. The laboratory comparison of toolmarks and firearms evidence is done using visual, stereomicroscopic and brightfield microscopy methods.
A firearms criminalist also examines firearms and their components (e.g. silencers) for proper functioning, an important aspect in accidental discharge cases. Muzzle-to-target distance determinations, traditionally involving clothing items, can be estimated by the firearms examiner with the proper firearm and ammunition. In cases of serial number restoration, the criminalist takes advantage of chemistry and metallurgy in an attempt to recover obliterated or otherwise removed serial numbers.
Questioned documents
A questioned document may be any object upon which there are character markings that are in doubt. This usually involves written and machine-printed materials on paper but may include any markings made on an object, such as paint or blood written on a wall or floor. For written documents, the examiner is concerned with the identification and individualization of handwriting and handprinting. In order to ascertain the authenticity or source of the questioned document, examiners may need to identify and decipher indented writings; identify and elicit information from altered documents, including additions, deletions, erasures, burning and fabrications; and identify and compare inks from multiple types of writing instrument and printed documents.
Machine-generated documents have changed rapidly with advancing technology, offering more challenges to the document examiner. Today’s technology has provided document examiners with greater resources for examination and comparison. It has also added questioned documents, such as credit card evidence, which includes card embossing, magnetic strip decoding and duplicate copy signatures; computer generated documents, which includes printed material and data files; and photocopied evidence.
As with trace evidence, preliminary examinations for the questioned document begin with visual and stereomicroscopic inspection. Advanced techniques in microscopy and infrared (IR) and alternate light source (ALS) imaging are heavily relied upon, especially for altered documents. Image capturing through digital cameras and importation into graphics programs for enhancement are also utilized. Chemical methods, such as TLC, and instrumental methods, such as spectroscopy, are used in the comparison of inks and dyes.
Reporting and court testimony
Once the work of a criminalist is completed, whether at the crime scene or in the laboratory, the results of the examinations must be communicated. This is accomplished through written reports. The laboratory reports should include the date, requesting agency and case/file number, the items received, the examination methods, the results of the analysis, and the opinion and signature of the examiner. The issued written report becomes a legal document that can be introduced and used as evidence in the courtroom.
On occasion, testimony will accompany the written report in the courtroom. Testimony by an expert witness can provide the judge and/or jury with an in-depth explanation of the examiner’s findings and opinions. Of course, the breadth of subject matter may be limited by the judge’s or attorney’s questions. The criminalist must qualify as an expert witness each time he or she testifies through a process of voir dire.
Concluding Remarks
The future of criminalistics will be an exciting one to watch. With the aid of the spectacular advances in science, criminalistics will continue to improve its use of technology and provide more answers from physical evidence examinations to previously unresolved questions. As the technology changes, so, too will the quality of the profession. Laboratory accreditation, which began as a voluntary program, is now an essential criterion for an operational crime laboratory in the United States. Certification of criminalists, whether general or in a specialty area, is currently voluntary and will likely shift to one that becomes essential in the years ahead.
Criminalistics is without a doubt the most diverse specialty in the forensic sciences. The variety of physical evidence items examined in criminalistics makes it a challenging and rewarding professional occupation for many.
