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. For Examples;
👉 Clothing is an excellent source of trace evidence.
👉 Microscopic and macroscopic substances may cling to clothing by static electricity or become caught in the fabric.
👉 Useful evidence is most likely to be found if the clothes are collected from the suspect or victim as soon after the crime as possible.
👉 Small items of evidence no bigger than a fiber may easily be dislodged from the clothing and lost.
✅ Shoes and other footwear are valuable items of evidence.
✅ They may have dust, soil, debris, vegetation, or bloodstains on them.
✅ In addition to the presence of trace evidence, shoes and other footwear are useful in shoe impression evidence comparison.
✅ Careful examination of the soil might lead to determination of the path that a suspect took.
🔬Trace Metal Detection
✔ The trace metal detection test, or TMDT, has been used with mixed results.
✔ The solution is sprayed on the subject’s hands and observed under ultraviolet light. The presence of dark areas indicates the location of metal.
✔ The TMDT is commonly used to test whether a subject recently held a metal object, such as a weapon.
🕴Evidence from the Body
✅ Useful trace evidence may be discovered by a careful examination of the suspect and/or victim’s body.
✅ Hair is sometimes found on the victim’s body in rape cases.
✅ A close examination of the head, ears, fingernail scrapings, and hands may yield traces of debris from a burglary, assault, or other crime in which there was contact between the subject and another person or the crime scene.
📑Other Objects as Sources of Trace Evidence
✔ Trace evidence may be present on tools and weapons, as well as other objects.
✔ Tools used in burglaries may contain traces of building material, metal shavings, paint, and so forth. Similarly, a weapon such as a knife may have hairs or fibers present that may prove to be useful evidence.
✔ Larger items may be fruitful sources of trace evidence, for example, a vehicle from a hit-and-run accident.
📩Collection and Preservation of Trace Evidence
• Small items of evidence should always be double packaged. Double packaging means that the evidence should be first placed into an appropriate container and secured.
• As with all evidence, the investigator or crime scene technician must be concerned with various legal and scientific aspects of collection and preservation of trace materials.
• It is obvious that if evidence needs to be mailed or sent by a parcel carrier, extraordinary care must be taken to preserve fragile substances properly.
• Control or known samples are required in all cases. The investigator should make every attempt to collect a sufficient quantity of known material to be submitted with the items in question.
• The known exemplars must never be packaged with the questioned samples. This separation is necessary to avoid cross contamination of unknown by known specimens.
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