Sources:“A Closer Look On Forensic Science“ written by Archana Singh
At a crime-scene, tiny fragments of physical evidence such as hairs, fibers from clothes or carpet can help tell the story of what happened. These are referred as trace evidence. Trace evidence can be transferred when two objects touch or when small particles are disbursed by an action or movement. For example, paint can be transferred from one car to another in a collision or a hair can be left on a sweater in a physical assault. This evidence can be used to indicate that a person or thing was present. It can also help in reconstruction of crime scene.
There are some examples of Trace evidence, such as; Fibers, hair, soil, wood, gunshot residue and pollen. These are a few examples of trace evidence that may be transferred between people or objects at a time of crime. A famous Principle is given by Dr. Edmond Locard ,” Every Contact Leaves Traces” in the early 20th Century. He showed the importance of trace evidence in criminal investigations. Investigating officers can develop a link between suspect and a victim to crime scene through trace evidence. Since then, trace evidence is used by forensics experts to solve the crime and to reconstruct crime scene.
🗼 Building materials of a wide variety may be encountered in burglary cases.
🗼 Materials such as stucco, cement, brick, mortar, plaster, plasterboard, wood, and paint constitute evidence generally considered as building materials.
🗼 This type of evidence is most likely found on the clothing of burglary suspects, in their cuffs, pockets, and shoes.
🗼 Bits of paint, plaster, wood, and even glass may become attached to the tool.
♨️ Chemical properties such as solubility and composition can indicate the type of paint and identify the pigmentation and fillers used in the manufacturing process.
♨️ Paint evidence is frequently recovered in hit-and-run accidents, burglaries, and forced entry cases.
♨️ Paint and other protective coatings such as lacquer, enamel, and varnish can be identified by physical and chemical properties.
♨️ Physical characteristics such as color, layering, weathering, and texture are useful in characterizing this evidence.
🛑 Rust stains may sometimes be confused with bloodstains. However, rust can easily be differentiated from blood by a simple chemical field test.
⚓ Filings, shavings, and other metal particles can easily be identified chemically or spectrographically.
⚓ Metal filings located in the jaws of pipe wrenches are fairly common sources of this type of evidence.
⚓ The wrench is used as a burglary tool by placing it onto a doorknob. Metal filings present in the teeth can be compared to those from the doorknob.
📛Textiles and Fibers
🧣 Fragments of cloth may become evidence in a wide variety of cases.
🧣 Torn fabrics have been examined in murder cases in which the victim was tied and gagged with torn fabric.
🧣 In burglary cases in which a suspect left a small torn piece of clothing caught at the point of entry.
🧣 Properties such as color, type of cloth, dye, direction of fiber twist, and thread count are useful in characterizing the evidence.
⚾️ Buttons come in a very wide range of sizes and patterns; only in exceptional cases is it possible to match a button with the buttons of a particular garment. When a button is torn off, generally the thread and sometimes a piece of fabric may be present.
⚾️ If a piece of broken button is discovered, it is possible to match the broken piece physically with another portion of the button.
〰️Cordage and Rope
🎗 In cases of strangulation it may be possible to identify epithelial (skin) cells attached to the cordage.
🎗 Pieces of string or rope are sometimes found at crime scenes.
🎗 Properties that can be examined include the material from which the cordage is manufactured, the number of strands, direction of the twist in the rope, color, diameter, weight per unit of length, etc.
🎗 Rope and cordage evidence can be compared with exemplars for similarities.
🚬Cigarettes and Tobacco
🚬 Cigarettes, cigarette butts, tobacco, and ash are frequently found at crime scenes and just as frequently overlooked as potentially useful evidence.
🚬 From the point of view of forensic science, very little work has been done in the identification of tobaccos.
🥢 Matches found at a crime scene may be from smokers or from suspects who used them to light their way. Several may commonly be found in burglary cases.
🥢 The type of wood, microscopic appearance of the cardboard, color, dimension, and shape are useful in comparing a burned match with some exemplars associated with the suspect.
🥢 The surface of a single match is usually too small to find sufficient detail to identify a latent fingerprint.
📥 Burned documents can be deciphered, provided they are reasonably intact.
🗞 If the paper has been reduced to ashes it is not possible to determine any writing.
📥 For this reason, it is particularly important to exercise extreme care when collecting, preserving, and transporting this type of evidence.
📥 Burned papers and charred documents are sometimes found in arson investigations or in instances in which an attempt was made to destroy records by fire.
🕳 The composition of ash will vary greatly depending upon the source.
🕳 It can sometimes be identified microscopically, chemically, or by means of spectroscopy.
🕳 However, the source of the ash may prove difficult to determine.
🕳 One type of ash common in arson cases is the residue of burned highway flares.
🕳 This ash contains a significant level of strontium, responsible for the bright red color of the flare.
💩 Soil evidence may be encountered in a wide variety of criminal investigations.
💩 It may be found on shoes, clothing, or the underside of motor vehicles and is useful in tying the suspect or victim to a location.
💩 Soil is a mixture of decaying and weathered rock and decomposed organic material known as humus.
💩 It contains a wide variety of minerals such as quartz, feldspar, and mica as well as partially decomposed leaves, pine needles, pollen grains, and other plant fragments.
🌴 As evidence, wood may be present as sawdust, splinters, chips, large pieces used as assault weapons, etc.
🌴 Evidence may be present at the crime scene, on a suspect’s clothing, or in a wound. Wood may also have tool marks.
🌴 Wood may be divided into two types: hard woods and soft woods.
🌴 It is possible to determine the type of wood and often the type of tree from pieces the size of sawdust particles.
☘ A wide variety of materials of plant origin may be useful sources of physical evidence.
🌿 Besides wood, leaves, seeds, bark, twigs, and pollen are sometimes collected as evidence.
🍀 They may be attached to clothing, found in a vehicle, or present on a weapon.
🌾 Pollen is a useful material for determining whether a subject was present in an area where flowering plants are located.
🥂 Glass may be useful evidence in a wide variety of cases.
🚌 Hit-and-run cases often have headlamp glass or windshield glass present, burglaries frequently involve window glass, and bottle glass is sometimes found in assault cases.
🗯 Broken glass may yield information about the direction and speed of a projectile and, in the case of multiple projectiles, the sequence of events.
Examples of Trace Evidence