The Hidden World of Trace Evidence: How Tiny Clues Can Solve Big Crimes
Written By
Ms. Vanshika Adhikari
Member, Shivi Forensics
Introduction
When thinking about evidence it is usual for fingerprints, DNA and weapons to be the first things that come to mind. However a crime scene may also contain another type of evidence which's very small and generally invisible to the unaided eye: trace evidence.
A single hair, a fibre, a piece of glass a spot of paint or a grain of soil may at first seem unimportant. However such small items can help investigators in making links between people, objects and places.
The National Institute of Standards and Technology (NIST) says that trace evidence consists of amounts or fragments of materials for example fibres, hair, paint and glass which might be transferred during an event. Forensic scientists create techniques for detecting, measuring and analysing these materials.
What Is Trace Evidence?
Trace evidence refers to evidence which occurs as a result of the transfer of small quantities of material and is closely linked with Locards Exchange Principle, a basic idea in the field of forensic science.
The principle is usually stated as "Every contact leaves a trace”, when someone comes into contact with another person, an object or an environment there may be a transfer of material in either direction.
For instance someone walking through an environment might pick up small particles onto their shoes. In the way fibres from their clothing could possibly be transferred as a result of physical contact.
Even if the transfers are very small they can prove to be valuable when they are properly gathered studied and interpreted.
Hair: A Common Trace Material
Hair is often found as a result of examinations and can be retrieved from clothing, surfaces, vehicles and other items connected with the investigation.
Forensic hair examination can include an examination and the comparison of various characteristics and the FBIs procedures for its forensic laboratory cover the microscopic examination, identification and comparison of hair evidence as well as the methods for preparing hairs so that they can be analysed by DNA techniques.
Hair evidence has to be interpreted with care since microscopic features on their own should not be taken as proof that a specific person was the one who left it. If suitable biological material is available DNA analysis can offer information.
It shows that hair can be an example of how trace evidence may help in an investigation even if it doesn't itself provide the whole answer.
Fibres: Tiny Threads of Evidence
Fibres may come from clothing, carpets, upholstery, ropes and other textile materials. Since they can be transferred as a result of contact they might yield information regarding possible associations between objects, people and locations.
Forensic examiners are able to examine fibres using a microscope. Might use further analytical techniques when it is appropriate to do so. The procedures used by the FBI for examining fibres include examination as well as instrumental methods such as microspectrophotometry and FT-IR.
It is important to note that the presence of a fibre does not necessarily mean that a specific person has committed a crime; rather scientists assess whether the observed characteristics are compatible with a known or questioned source and then interpret the findings in the context of the case.
Glass: Fragments That Can Create Connections
Glass is also a significant type of trace evidence and may be found in cases which involve vehicles, windows and other glass objects.
Small pieces of glass can be found in clothing, footwear, vehicles or in the surrounding area. Nowadays forensic laboratories use a variety of methods when examining glass, such as physical and chemical characterisation. For example NIST carries out research into the analysis of fragments of glass and elemental analysis techniques.
Comparing the questioned glass samples with the known ones can enable investigators to determine if the materials are consistent with each other.
Soil: A Clue From the Environment
Soil is another type of trace material which may be used to link an object or a person with an environment.
The soil is made up of a mix of minerals and other substances and its properties can differ from one place to another. Dusty particles can become attached to boots, clothing, vehicles or tools.
Soil can therefore be considered as part of an extensive investigation. The FBI includes soil and other materials derived from sources among the types of evidence it examines in trace-evidence work.
Soil evidence like all trace evidence should be interpreted in a scientific way rather than being taken as automatic proof of a particular location.
Paint and Other Trace Materials
Paint fragments can also serve as evidence especially when detectives are looking into damaged vehicles, painted surfaces or objects that were involved in an accident.
A small piece of paint can provide details regarding its chemical properties. The forensic scientists will use microscopy and instrumental analysis to examine and compare the samples depending on the material in question and the circumstances.
Trace-evidence examination does not stop with hair, fibres, glass and paint; the NIST and FBI have also identified materials such as tape, building materials, cordage and geological materials as areas involving trace analysis.
How is trace evidence examined?
The scientific analysis of trace evidence starts well before the sample gets to the laboratory.
When at the crime scene evidence has to be recorded, gathered, placed in suitable containers and kept to minimize the chances of it being contaminated or lost. The guidance from the NIJ stresses the need to keep the integrity of evidence.
In the laboratory the method of examination will vary according to the type of material; microscopy can be of use for observing its features whereas spectroscopic, chemical or other analytical techniques can give further information.
Forensic research today is placing an emphasis on enhancing the accuracy and reliability of such examinations. As part of its trace-evidence programme NIST carries out research on glass, hair, fire debris and polymeric materials.
What is the importance of trace evidence?
What makes trace evidence really strong is the fact that it can establish connections.
A fibre could possibly link clothing to an object. Glass fragments can be compared with the suspected source. Soil might yield information concerning an environment. Hair can provide biological information.
Forensic conclusions must be based on evidence. The forensic standards developed by NIST specifically concern themselves with the interpretation and reporting of comparisons involving trace materials such as fibres, glass, hair, paint and tape.
Trace evidence is therefore most effective when it forms part of a body of evidence rather than when it is treated as a single "magic clue."
Forensic science does not always involve discovering something obvious; at times it is the tiniest fragments that can give important information about what took place at a crime scene.
Things like hair, fibres, glass, soil and paint may appear to be ordinary in life but they can become valuable elements in an investigation when examined forensically.
The time you see a forensic investigator carefully collecting a tiny particle from a crime scene remember:
In the field of forensic science the tiniest piece of evidence at times is enough to help establish the most significant facts.
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