Wherever we go, whatever we touch or with whatever we come in contact with; we leave a trace or mark on it. And in the case when a crime is committed the number of such traces increases due to the intensity of the crime. This evidence can be at times very small and almost invisible to the naked eyes, such as hairs, fibers, glass, paint, etc. Though small, this evidence if analyzed properly can help in making the picture clearer and facilitate the investigator in solving the case.
In this article, the author has explained Trace’s evidence, Locard’s Principle of Exchange, and analyzed the common types of trace evidence used in investigations.
Trace Evidence refers to the small or even microscopic things that are found at the scene of the crime and can be used for investigation. Like other Forensic evidence, these are also used to link the victim, the suspect, and the place of crime together. Criminal cases are like a puzzle and trace evidence can help fill the gaps in them. Though this evidence is microscopic themselves but can help reveal information big enough to narrow down the list of suspects. Generally, Trace evidence is used along with other evidence but at times when no other evidence is available, these are the only source of information for an investigator.
Whenever a crime is committed the criminal unknowingly leaves a trace at the scene of the crime, and more violent the crime there are higher chances of such traces being left behind. Therefore, an investigator has to examine and analyze the scene properly and collect all possible trace evidence. These trace evidence is not definite and may depend on the situation, circumstances, and scene of each crime. If analyzed properly these can reveal crucial information like the number of criminals, the vehicle and weapon used, and the route used to enter and exit the scene.
Locard’s Principle of Exchange
Dr. Edmond Locard was the director of Crime Laboratory in Lyon who came to be known as the Sherlock Holmes of France. In the early 20th century he formulated the theory which became the basic principle of forensic science. i.e Every contact leaves a trace. This is popularly known as the Locard’s Principle of Exchange.
According to Locard, keeping in mind the intensity of the crime, it is impossible for a criminal to not leave a trace or mark of his presence. A person will always leave something and take something from the scene of the crime, which might not be visible to the naked eyes but exist there. As per the theory whenever someone touches something, comes in contact with something, or someone, he will always leave something behind. It can be fingerprints, hairs, or even fibers; these minute details are the silent witness of the crime. And though human witness may not be present, this evidence is always present at the scene.
Types of Trace Evidence
Several trace evidence exists at a scene of the crime. However, most common among them are fibers, glass, hairs, soil, paint, gunshot residue, fire debris. Hairs are considered to be very useful trace evidence as they originate from the body and can be associated directly to the suspect, animal, or victim, making things clearer. Other sources such as fiber, glass, and paint are somewhat different from hairs as trace evidence because these are generally not in their natural form and are manufactured products that too in a large quantity. This means that the analysis of these traces only suggests their likely source. We shall discuss these trace evidence in a bit detail below.
Fibers are a thin thread generally used to make clothes and similar materials. It can easily be transferred to other objects or cloths on coming in contact. Fibers are of three types natural, manufactured, and synthetic depending on how they are made. This makes it useful for trace evidence. However, it is necessary to collect them at the earliest as they are usually lightweight and can fall or get brushed off from the cloths quite easily. Therefore, investigators focus on the most probable places to search for these fibers on the crime scene, such as the victim’s cloth, carpet, or even his body.
Like most other trace evidence it is collected using tape, tweezers, or vacuums. The first recommendation to use tapes for collecting trace evidence was given by Dr. Max Freisulzer.  However, using tapes is not considered proper as there are chances of damage and cross-contamination.
Due to the different types, ways to produce, and color of the fibers it is advantageous to use it as trace evidence because it narrows down the suspected sources to a great extent. However, even after fiber testing, fluorescence testing, melting point testing, and chemical analysis, it can only be said that the sample fiber and the fiber collected from the suspect have a common origin and nothing more. This is because these fibers are produced in large quantities and used in clothes worn by several people. The use of fiber as trace evidence is of prime importance in cases where the fiber is not the one commonly in use.
Glasses are found almost everywhere, in our house, office, shops, and even in vehicles. This is the reason why glass is considered a commonly used trace evidence. In cases of hit and run or housebreaking, mostly the glass gets broken, leaving several fragments on the scene of the crime. These fragments are so small that they even might get to the hair, skin, shoes, and clothes of the victim and suspect. Testing the samples collected from the scene can help a lot in narrowing down the suspects. This is because a variety of glasses such as eyewear, containers, tablewares, etc exist, and once the type of glass is known it becomes easier to point out certain probable sources.
To find this evidence, magnification and lights are used; and then they are collected through tweezers and tapes. However, due to the abovementioned reason tapes are not considered the ideal preference. When a fragment of glass is collected and sent for testing, its color, thickness, density, solubility, patterns, fracture marks are checked primarily. Then the sample is matched with the suspected source and in case both the glass samples match, it can be said that both have originated from the same source. In the process, several tests such as X-ray fluorescence, spectrometry, and Glass Refractive Index Measurement are conducted.
People shedding hair is not an unusual thing. These are unintentionally left in places we visit and in cases of struggle or assault get transferred from one individual to another. It is this ease of transfer that makes it the most often used trace evidence and useful in the investigation. Also, as compared to other trace evidence hairs are easily discoverable and do not get destroyed easily. It is worth noticing that Richard E. Bisbing has very well pointed out that the structure of hair can be compared with a usual pencil. Wherein the outermost layer of the hair i.e cuticle can be compared to the paint of the pencil, the middle part i.e shaft to the wood, and the inner part i.e medulla to graphite. And in both pencils and hair, the primary difference is noticed based on their color.
Proper testing of hairs can help differentiate between a human’s and an animal’s hair; and also between hairs of different individuals. Sample of hairs can facilitate in determining the color, method of removal, chemical composition as well as the body area from which the hair originated. Samples can also be tested to know about any disease, treatment, bleach, or damage to the hairs. This information combined can help in decreasing the number of people suspected. Once the hair samples are tested, they are compared with the hairs of those suspected. In case both the hair, samples are found to be similar using microscopic techniques and chemical analysis, then it can be said that sample hairs used as trace evidence could have originated from that particular individual. And in case the samples do not match it is concluded that both of them originated from different individuals. It is one of the drawbacks of using hair as trace evidence that though it may ensure similarity but it does not give any surety.
One of the oldest cases in which hairs were used as trace evidence was the murder of the Duchesse of Praslin in the year 1847. In that case, her dead body was found in her hotel room in Paris. The loaded gun of the Duke was found under her body with the bit of the Dushesse’s hair on the handle. This indicated that she was stuck with it. The Duke could not explain how his pistol’s handle had her hairs on it and therefore, was found guilty and imprisoned. 
When two objects interact, both or either one of them leaves a mark or impression on the other. Though such marks can be made even at hard surfaces it is easy to find such marks on soft surfaces like soil. These marks can be of anything however the investigator primarily looks for the shoe or tire marks. Shoe marks once discovered at the scene of the crime can help tell us a lot about the size and company of the shoe as well as the route of entry and exit of the suspect or suspects depending on the number of shoe marks. Similarly, tire marks are also of use in determining the size, design, pattern, and depending on them the type of vehicle as well as the rote of the entry and exit of such vehicle or vehicles.
These marks are generally collected by taking their photographs but at times can also be collected by using plaster materials. It is necessary to collect any such mark at the earliest as the shape of soil changes easily leading to loss of such trace evidence. Soil can help in determining the suspects that could have been at the scene of the crime. Once a list of suspects is prepared the soil found on their shoes or tire of the vehicle is compared with the soil at the scene of the crime. These are compared on the ground of color, composition, presence of minerals, and other materials. And in case no difference is found between the soil, it can be said that soil found on the shoes or tires of the suspect’s vehicle could be from the scene of the crime.
Paint is the substance used to cover the surface of an object or thing with a particular color to decorate or protect it. Since it can also be found on almost every object it is a widely used trace evidence. The major reason why paint is useful evidence during an investigation is that the colors are almost innumerable which brings down the number of suspected objects, then as different types of paints are used on different objects it can also help in determining the object narrowing the suspected objects further. Also, when an object is painted again and again several layers get created. By analyzing and comparing the sample and the suspected object using the number of layers can at times lead to the conclusion that the sample originated from the particular object. It is worth noticing that in cases of hit and run, sometimes paint can even be used to determine the model and year of the vehicle.
While collecting the paint, the investigator needs to be careful to get all the layers of the paint without damaging them. Microspectrophotometer is generally used then to determine whether the color of both the paint matches properly or not. Then the thickness, layers, texture, and chemical composition are tested to determine whether the two paints originated from the same source or not.
Other commonly used trace evidence includes gunshot residue and fire debris. Analyzing gunshot residues can help in determining the type of gun used and the distance between the suspect and victim at the time of the attack. Similarly, analyzing fire debris by way of the heated headspace method and passive headspace method can help in determining whether any ignitable liquid is present in the debris or not.
In Delhi, the Investigation Agency had to face a problem of determining whether the death was a suicide or murder. The victim was a 32-year-old married woman who according to her husband had an illegitimate relationship with the suspected person. He disclosed that on the day of her death, his son while leaving for his tuition saw her and the suspect arguing. And when he came back, he found the door locked and informed his father who in turn informed the police leading to the investigation. The police found her dead with a rope tied around her neck. But it was informed that she had no reason to commit suicide. The Post mortem report suggested the reason of death as strangulation.
Later the Investigation Agency inquired the suspect and seized his shirt which had an unidentified stain and a torn buttonhole, indicating a struggle. On testing, it was found that the unidentified stain with a high level of sulphide ion and mercury, was the same material, found on the scalp hairs of the victim. This clarified that the suspect was present at the scene of the crime and came in contact with the victim. It was realized that the said material was vermilion applied by the deceased that left a mark on the suspect’s cloth, and later worked as trace evidence in solving the case.
Trace Evidence includes almost all the small or microscopic objects found at the scene of the crime, which may have been left, shed, or transferred during the commission of the crime. These play an important role in the investigation because they can help in narrowing down the number of suspects. However, it must be noted that these unlike fingerprints or DNA do not create a direct link between the victim and the suspect or identify the criminal. They only help in determining who might be the criminal but rarely give a surety. Since they do not help in identifying the criminal directly, they are often underrated. However, it can not be forgotten that in an investigation all the evidence is necessary to catch the criminal.
The importance of trace evidence is linked to the development of science. As with its development, it gets easier to collect, test, and analyze the trace evidence. Therefore, the importance of trace evidence neither had been what it is today nor will be limited to what it is today, but will increase with the advancement of science.
Frequently Asked Questions
- What is meant by Trace Evidence?
- What is the Exchange theory given by Dr. Edmond Locard?
- What are some commonly used Trace Evidences?
- Which is the most often used Trace Evidence and why?
- Why is Trace Evidence underrated?
-  –, ‘Introduction’ Shodhganga, available at https://shodhganga.inflibnet.ac.in/bitstream/10603/211347/9/09_chapter%201.pdf
-  John Fuller, ‘How Locard’s Exchange Principle works’ How Stuff Works, available at https://science.howstuffworks.com/locards-exchange-principle2.htm
-  Richard E. Bisbing, ‘Trace Evidence in real crime laboratory’ Springer, available at http://eknygos.lsmuni.lt/springer/658/265-290.pdf
-  Ibid.
-  –, ‘A Simplified Guide to Trace Evidence’ Forensic Science Simplified, available at http://www.forensicsciencesimplified.org/trace/TraceEvidence.pdf
-  Supra note 3
-  –, ‘Trace Evidence Analysis’ NJSP, available at https://www.njsp.org/division/investigations/trace-evidence.shtml
-  –, ‘ How it’s Done’ Forensic Science Simplified, available at http://www.forensicsciencesimplified.org/trace/how.html
-  Sweta Sinha et. al., ‘Forensic Identification of Sindoor Stain on Cloth as Trace Evidence Analysis’ Medwin Publishers, available at https://medwinpublishers.com/IJFSC/IJFSC16000186.pdf