Hair - Analysts can tell investigators if individual hairs are human or animal, and in the case of human hair, where on the body the sample originated. Samples can be tested to determine the color, shape and chemical composition of the hair, and often the race of the source individual. The presence of toxins, dyes and hair treatments are noted. This information can assist investigators in including or excluding particular individuals as the source of the hair. If the hair still has a follicle (root) attached, DNA testing may be used to identify an individual; otherwise, hair comparison is typically used only to exclude. Collection: Collected samples are sent to the laboratory along with control samples from a suspected individual. Control samples should include hair from all parts of the head and, for pubic hair, the area should be combed for foreign hairs prior to sample collection. Hair samples are primarily collected using tweezers. Fiber - Fibers are threadlike elements from fabric or other materials such as carpet. Most are easily identifiable under a microscope. Fibers fall into three classifications: natural (animal or plant fibers like wool, cotton or silk), synthetic (completely manmade products including polyester and nylon) and manufactured (containing natural materials that are reorganized to create fibers such as rayon). Fibers are useful in crime scene investigation because their origins can be identified. A carpet fiber on a person’s shoe can indicate the individual’s presence at a crime scene. However, fibers are very mobile and can become airborne, get brushed off or fall from clothing. This mobility makes timely collection crucial to prevent loss of material or cross-contamination. Collection: Fibers cling to other fibers and hair, but may be easily brushed off. When approaching a scene, investigators will attempt to pinpoint the most probable locations for deposited fibers. For example, the carpeting under and surrounding a victim’s body, clothing from the victim or a suspected weapon are likely places to find fibers. Common collection methods include individual fiber collection using tweezers or vacuuming an area and sorting the materials at the laboratory. Trace evidence can also be gathered by tape lifting, however, this is not ideal due to the destructive nature of adhesives. Samples that potentially contain fibers should be separately bagged to prevent cross-contamination. References to collection and storage of fiber and hair evidence can be found in the Quality Documents Program, Laboratory Physical Evidence Bulletin #4. Glass - Glass can be used to gather evidence, for example collecting fingerprints or blood from a broken window; however, glass also has a place in the trace evidence section. Broken glass fragments can be very small and lodge in shoes, clothing, hair or skin. Gathering glass fragments from a crime scene can be valuable in determining end-use or connecting people and objects to places. For example, windshields have a different color and composition than a drinking glass or a lead crystal vase, so glass fragments on an individual’s clothing could be compared to those collected at a hit-and-run scene to determine if that individual was present.  Windshield fracture pattern. (Courtesy of NFSTC) Collection: Trace examiners may use magnification and light to find glass fragments on clothing, an individual or at a crime scene and extract those using tweezers. Tape may also be used to collect glass samples, but the residue left from the adhesive makes this a less desirable collection method. References to collection and storage of glass can be found in the Quality Documents Program, Laboratory Physical Evidence Bulletin #3. Paint - Painted surfaces are everywhere and the wide variety of layered colors, lusters and types often make paint high-value as evidence. For example, paint transferred when one vehicle hits another vehicle, a pedestrian or a building can be matched to potentially identify the car in question. In a property crime where a tool is used to break into a building, paint transferred to or from the tool can connect the tool to the location. Analyzing automotive paint can identify the make, model and sometimes the year of a vehicle. Collection: To collect paint, investigators document the scene, then peel off, or excise, small amounts of paint from the source, being careful to gather all layers. Samples as small as one square millimeter can be used for testing. For a car crash scene, paint samples from the point of contact would be photographed, collected and stored in such a way as to protect the edges for further examination. This is particularly important when examining for fracture matches. Paint samples are typically collected by scraping small sections down to the metal or original surface or using tweezers to collect chips already dislodged. References to collection and storage of paint can be found in the Quality Documents Program, Laboratory Physical Evidence Bulletin #2. Who Conducts the AnalysisMost large laboratories or laboratory systems have a trace evidence section. Analysts have a variety of backgrounds, but most require a degree in a natural science with additional certification or additional study in chemistry, particularly if the primary degree is not in chemistry. Certification is generally conferred on an individual who has achieved specific education, training, experience and performance on competency tests as designated by the certifying organization. Some areas of trace evidence have individual certification programs, which are facilitated by professional associations and boards. The American Board of Criminalists certifies trace examiners using a General Knowledge Exam (GKE) and specialty exams in fibers, hair and glass. How and Where the Analysis Is PerformedSince trace evidence covers a wide variety of subcategories, there is similar variety in the testing that is performed. Specialized testing may be done outside of the local laboratory at regional or national facilities. The type of test performed and the range of information provided vary by the type of evidence tested. For example, analysis of a strand of hair may yield information on the race and general health of the donor, while analysis of a paint sample would likely yield the manufacturer of the paint and its commercial use. Hair: Hair samples are tested primarily by microscopic comparison and chemical analysis. Microscopic comparison identifies the shape, color, texture and other visual aspects of the sample, while chemical analysis indicates the presence of toxins, drugs, dyes and other chemicals. In some cases hair is subjected to DNA analysis. Learn more about DNA ▸ Fibers: Trace evidence analysts often have only mere strands to work with. From these strands, fiber testing is done using high-powered comparison microscopes to compare texture and wear in a side-by-side assessment. Chemical analysis can determine the chemical composition of the fibers. In the case of synthetic fabric or carpet, this information can be used to trace the product to the manufacturer using standards databases, further enhancing the probative value of the evidence. Glass: Glass can yield valuable information through fracture marks, lines and patterns. Testing for unique characteristics such as color, optical properties and density can determine the type of glass, for example a window pane, vase or glass bottle. A detailed elemental analysis, including specific impurities, can be done using laser ablation mass spectrometry, induction-coupled mass spectrometry, X-ray fluorescence or other instruments. Glass shards can be used for sourcing the glass and also to collect potential biological evidence. (Courtesy of NFSTC) Paint: Powerful comparison microscopes are used to compare colors, thickness and layer patterns, and luster or to match fragments and tears. Chemical testing, such as Pyrolysis Gas Chromatography (PYGC) can be used to determine chemical composition, colors and pigments and other qualities. Microscopic comparison of paint samples can show layers of paint, primer, coatings, scratches and other damage that can uniquely match two pieces or otherwise provide class identification information. (Courtesy of NFSTC) Back to top of page ▲ An estimated 1,197,704 violent crimes occurred nationwide in 2015, according to the Federal Bureau of Investigation's Uniform Crime Reporting Program. Violent crimes are determined according to a Hierarchy Rule: murder, non-negligent manslaughter, rape, robbery, and aggravated assault. The collection, preservation, and forensic analysis of the evidence with most crimes are often critical in determining a person's guilt or a person's innocence. The forensic exam is beneficial to law enforcement and the medical setting to provide a comprehensive medical forensic examination with the collection of evidence knowing the patient's body is the crime scene. Evidence must be identified, collected, packaged, secured, and maintained correctly, then released to Law Enforcement following a strict chain of custody rules so that it can be analyzed appropriately and used later in legal proceedings. When collecting evidence, the examiner must wear gloves at all times and change them often utilizing the clean technique. Following proper collection, handling, and storage of evidence will reduce the possibility of cross-contamination or degradation of DNA.[1][2] Trace Evidence May consist of debris such as dirt, soil, sand, gravel, grass, leaves, twigs, adhesives and tape, fibers, glass, or bullet fragments. When trace evidence is identified, the following steps in the collection of the evidence is outlined below:
Biological Evidence May consist of blood, skin, hair, semen, saliva, and urine.
The same process for packaging, securing, and maintaining the evidence as outlined above is used for the collection of trace evidence.[4][5] Clothing Evidence Clothing that is worn by an individual at the time of the crime often contains physical or biological evidence that must be preserved. If the patient is wearing the clothes they had on during the assault, all items can be considered evidence. If the patient is not wearing the clothes they had on during the assault, clean clothing put on later by the patient, such as underpants in the case of a sexual assault, may still contain bodily fluids other than the patient's. The patient's clothing must be handled and examined carefully to avoid loss of evidence. Each piece of clothing must be dried thoroughly if wet or damp. Each piece must be identified, labeled with the patient's identifying information, date, time, and examiner's initials. All stains or tears to the clothing must be documented. When these steps have been completed, each piece of clothing must be placed in separate bags to avoid cross-contamination. The clothing placed in the individual bags must be identified, labeled with the patient's identifying information, the examiner's signature, initials, date, and time. Each bag is then placed in a larger bag, properly labeled with the patient's identifying information, the examiner's signature, initials, date, and time. When clothing is collected, it must be correctly identified, packaged, preserved, secured, and maintained until released to law enforcement with the proper chain of custody for further analysis at a forensic/crime laboratory.[6] Injury to the Body The forensic examiner will take a history from the patient to help guide in performing a detailed head-to-toe assessment to identify injury or findings to the patient's body. Injury or findings must be documented by taking photographs, measuring the injury utilizing measuring tools, and/or using age-specific body diagrams. The correct terminology must be used to describe injury and findings. For example, medical personnel confuses lacerations versus cuts. Lacerations are caused by blunt force trauma, and cuts are caused by sharp force trauma, usually by a sharp object. It is critical to correctly identify the injury and the mechanism of the injury:
Again to emphasize, when possible, the examiner may use a camera, measuring tools, and age-appropriate body diagrams to document the medical forensic examination. Keeping the Evidence Secure [7] Collection, preservation, and securing evidence are critical from the time it is collected. Completion of the chain of custody documentation is also critical. The chain of custody form must contain information about the evidence collected and must remain with the evidence until it is released to law enforcement. The patient's identifying information with the date, time, Law Enforcement involved with the case number must be included. Each person who has had contact or possession of a piece of evidence must be identified on the chain of custody form from the time it is collected and then released to Law Enforcement. If the chain of custody documentation is incomplete, inaccurate, or omitted, it will cause the evidence to be inadmissible in a court of law. Important Factors to Follow When Collecting Evidence [8] [9] Collect evidence correctly, preserve each specimen separately, use and change gloves often, avoid coughing or sneezing during the collection, use appropriate tools such as cotton-tipped applicators, sterile water, cardboard swab boxes, separate paper bags, and envelopes to prevent cross-contamination of samples collected. Allow swabs to dry thoroughly, dry with cool air only, no heat, package in a vented swab container boxes or paper. Do not use plastic. All these steps will preserve the integrity of the samples collected. To maintain accurate identification, each sample must be labeled with the patient's identifying information--patient's legal name, date of birth, medical record number, date, time, and the examiner's signature. The forensic examiner must be knowledgeable about the medical forensic examination and the different types of evidence of why, when, where, and how to collect, preserve, maintain and release the evidence. Many patients will present with a need for a medical forensic examination with the collection of evidence. Many professionals will be involved in the care of these patients; clinicians, nurses, advanced practice nurses, forensic nurse examiners, and other healthcare providers. The healthcare provider should have advanced training in the care and overall assessment of the patient. Ongoing education and training are important due to the ever-changing advances in treatment and technology and can be achieved by attending conferences, reviewing published research studies, and using current guidelines and recommendations. Each healthcare provider is an important member of the team to accomplish the best outcome for the patient and assist with future follow-up care and resources. Many patients will have law enforcement involved for investigative purposes and possible legal proceedings. The healthcare provider may be required to testify in a court of law at a later date, usually years later. A thorough examination must be performed, documentation completed, and the evidence collected at the time of the examination must be complete, accurate, and concise. |
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