SUBJECT FORENSIC SCIENCE Paper No and Title Module No. and Title Paper 7 : Criminalistics and Forensic Physics Module No. 11; Trace evidence Module Tag FSC_P7_M11 TABLE OF CONTENTS 1. Learning Outcomes 2. Introduction 3. Trace Evidence 4. Collection of Trace Evidence 5. Preservation of the evidence 6. Problems while collecting Trace Evidence 7. Summary
Ridge Characteristic 1. Learning Outcomes After studying this module, you shall be know about The importance of the trace evidence Various methods for collecting and preserving the trace evidence Problems faced while collecting trace evidences 2. Introduction The importance of the trace evidence in the field of criminal investigations came into picture in the early twentieth century. Since then these have been used to reconstruct the crimes so that a clear description of the people, places and the things involved in the crime becomes available. Such evidence include finger prints, fibres, paints, glass, gunshot residue etc to follow the criminals but these evidences have to be collected with a special care so that they are not destroyed and proper analysis can be done. The carelessness while collecting the evidence may lead to contamination and incorrect results. It is actually a physical contact between the criminal and the victim that results in the transfer of trace materials. Their identification and comparison associates the suspect to the crime scene under investigation. 3. Trace Evidence Trace Evidence refers to small samples of a substance, in particular, finger prints, fibres, hairs, glass fragments, soils, gunshot residue, paint chips etc. Dr. Edmond Locard, founder of the Institute of Criminalistics at the University of Lyon, France, showed their importance for the first time. He gave the famous Principle known as Locard s Exchange Principle, which states that every contact leaves a trace which means that the criminal will definitely leave a trace evidence at the crime scene. Most of the crime scenes do contain trace evidence left behind by the criminal unconsciously. These evidence serve many roles during an investigation like identifying the remains at the crime scene or reconstruct a crime. The presence of trace evidence is mainly dependent on the type of material to be considered as a trace evidence since some particles and substances remain on a surface for a longer time. This depends on the size, shape and the amount of the particles deposited. Smaller particles persist for a longer time in comparison to the larger particles. Also irregular surfaces such as wood collect smaller particles more readily than the smooth surfaces. Among the important examples of the trace material we have: Hairs (Human and animal hair): The examinations of the hairs determine whether the hair is human or animal. In case it is human hair one can determine the racial characteristics like body area, length, root type or any artificial treatment done on the hairs. If, the hair is of any animal species, then the species and breed of the animal can be determined.
Fig1: Some hair samples Fibres: The fibre examination can determine whether the fibre is natural or man-made. Its source can be determined by comparing it with fibres from a known source. Natural fibres are mainly from a plant or an animal source like cotton, silk etc. These can be detected easily by microscopy. But most of the fibres used in the garments now a days are synthetic. Standard samples are taken for comparison with suspect samples. Fig 2: Natural and man-made Fibres
Fabric: Fabric examinations determine whether the suspect fabric and a known piece of fabric are same in construction, color and composition. Feathers: Feather examination can determine the species of the bird after comparing with the known samples Glass: Since different types of glasses are produced in different ways, it is possible to determine the source from which the broken piece of glass used as the evidence, originated. One can easily come to the conclusion whether the glass under consideration is a window glass, in car windshields, or a vehicle s rear and side window glass. Fig 3: Analysis of a glass sample Paint: The analysis of the paint can be mechanical, physical and chemical. The analysis includes matching of flakes of paint, the exact composition of the paint, the texture, appearance, thickness and the pattern of the occurrence. Fig 4:Comparison of Paint Flakes Finger prints: Fingerprints are actually the best evidence as fingerprints can identify the person exactly, present at the crime scene.
Fig 5: Fingerprints Blood samples: The shape of the blood samples can actually tell as from what height they have fallen down. DNA from blood samples can be extracted to simplify the identification from crime scene. Fig 6: Blood Sample 4. Collection of Trace Evidence After the location of the evidence from the crime scene is noted, the collection process for the evidence begins. There are two important precautions to be taken into account while collecting the evidence: The samples of trace materials like hairs to be tested should be carefully collected and along with this, the carrier on which the material is found like the bedding, clothing, should also be collected.
Before collecting the evidence, several methods are employed to detect the evidence that include visual searches by oblique lighting, Ultraviolet light sources, lasers etc and by magnification. While collecting the items, one must be careful to prevent contamination and loss of the evidence. For that purpose, the contact between the item to be collected, as trace evidence and other people should be avoided and the investigating team should be in appropriate apparels. First, the most fragile and the evidence that will easily get destroyed are collected. Then those evidence are collected that need to be moved. The methods used for collecting should direct and simple. The methods usually depend on the type of the evidence to be collected and also on the place or the carrier the trace is to be collected from. The tools used for the collection include : Knife, tweezers, plastic containers with lids, scalapel, scissors, comb, filtered vacuum devices, ultraviolet light etc. The following techniques are used for collecting the evidence: Picking: The evidence is separated from an item using clean forceps, tweezers, scalapel,knife etc. Lifting: An adhesive such as a tape is patted or rolled on the item causing the trace material to stick to the tape without overloading it. The collected material is lifted and placed on either a transparent plastic sheet, a glass slide or glass petri dishes as it protects the sample from getting contaminated and can be easily removed for comparisons. But, these adhesive materials should be maintained so as to avoid any contamination. Scraping: Tools like a clean spatula are used to remove the trace material from an item to a clean paper which is immediately sealed to avoid sample loss. This is usually conducted in the laboratory to avoid the risk of contamination. Vacuum Sweeping: A vacuum cleaner with a filter trap is used to collect evidence from the crime scene. The filter along with its contents are immediately packed to avoid losses. The filter, vacuum parts should be cleaned thoroughly for other investigations. Such technique results in the collection of large amount of evidence. Combing: A clean comb or brush is used to collect evidence from hairs and fibres of the individual. The comb as well as the material collected should be packed together. Clipping: Nail clipping is used to recover the trace evidence from fingernails. The fingernails are clipped using clean scissors or clippers and then packed in clean paper. Fingernails can also be scrapped for obtaining the evidence from under the fingernails. Solvent extraction: In certain cases that involve grease or oil, a solvent extraction is used to collect the evidence.
Fig 7: Methods for collecting the evidence 5. Preservation and packaging of the evidence and its carrier The preservation and packaging of the trace evidence and the carriers varies from material to material. The most important step among the preservation of the evidence is to take a photograph of all the trace evidence from criminal investigation sites, while still in the place. All evidence packages should be sealed properly so that the samples are not tampered, contaminated or harmed, as might be the case if left open. Very small and loose trace materials should be kept in unused containers like paper packets or petri dishes, which are further secured in a paper bag.
Large items or the carriers like the clothing; bedding etc. should be kept separately in unused packaging material. If the clothing or the bedding is wet, then it should be dried quickly without exposure to either heat or sunlight. This is done in a secured area so that no evidence is either lost or gets contaminated. Also, an arrangement for collecting any trace evidence that falls from the carrier while drying is also made during the procedure. Certain manageable carriers or items at the crime scene that have got quite visible and firm trace evidence are documented, packaged and are transported to the laboratory. If there are items or the carrier at the crime scene that bear trace materials which can be easily lost or the carrier itself cannot be transported, then they are documented are collected by an appropriate method. Fig 8: Preservation of the evidence Some examples for collection and preservance of evidence: If there is gunshot residue on the clothing of the victim, then it is collected in a sealed paper bag to avoid contamination with the presence of other materials. If illicit drugs are there, then they are collected with a knife and each of the drugs is sealed in a separate, sterile container. The beddings, clothing s, towels etc are taken and packed separately. Body fluids like semen, saliva, vomit etc are collected with tweezers, scalpel, sterile cloth squares, ultraviolet light while blood samples are collected by blood collection kit.
If there are hairs and fibres available as trace materials on the crime scene, then they are collected using comb, tweezers and filtered vacuum device and then sealed in paper packets. The trace evidence remains in a secured area where a control on the access to the area is maintained to protect it from loss, damage or contamination. It is documented and kept in custody till its submission into the court. The security is the responsibility of all the persons involved in collecting, packaging, sealing, transporting and preserving the evidence. 6.Problems that occur while collecting the evidence Mishandling of the evidence or presence of certain near by objects can contaminate the evidence like mixing of blood of the suspect and the victim. Fingerprints and DNA traces are much more vulnerable to what we call as false positives. By false positive we mean a type of error, which occurs when, an analysis gives positive result or incorrect result which should not have given. These mostly occur in drug analysis, detection and analysis of bloodstains. 7. Summary The trace evidences are the minute samples of substances like hairs, fibres etc which give a complete description of the people and the places involved in the crime. Dr. Edmond Locard, gave the famous Principle known as Locard s Exchange Principle, which states that every contact leaves a trace. The nature of the trace evidence is quite variable and is found almost at all the crime scenes. Usually, in forensic physics laboratories, the analysis of both microscopic as well as macroscopic trace evidence is done. These evidences have to be then protected and packaged carefully lest they get contaminated or destroyed before their submission to the court. The most important step among the preservation of the evidence is to take a photograph of all the trace evidence from criminal investigation sites, while still in the place.