The evidence is general is anything that tends to prove or disprove some extent under investigation or consideration. Physical evidence is evidence having a physical or material quality- a tangible article, regardless microscopic or macroscopic. It includes any and all objects, living or inanimate solid, liquid or gas.
The physical evidences play a big role within the investigation of crime. According to section 157 of Indian Cr. P. C., the crime scene being the richest source of various types of evidences must be searched thoroughly.
In scientific investigation, physical evidences play an important role in linking the suspect and victim with each other or with the scene of crime. Evidences are recognized, collected from a crime scene and sent to the laboratory for scientific analysis according to the requirements of the investigative officer. He must also be skilled in the handling, collection, preservation, packing and forwarding of such evidence. The investigator must maintain the chain of custody of the evidence to ensure its evidential nature.
Physical evidence of macroscopic nature may quickly catch the attention of the investigator. But generally the evidence, which is microscopic in dimension, is most likely to overlook by investigators, as they are difficult to locate.
SOURCES OF PHYSICAL EVIDENCE
The physical evidence are often obtained from three main sources
- The scene of crime
- The victim if any and
- The suspect and his environment
The crimes against property will usually involve only 1 and 3 sources mentioned above; whereas crime against the person will involve all the three sources.
Forensic scientists have tried to classify evidences in different ways on the basis of several different perspectives. Some of the classification systems are more useful than others. But none of the systems, however, can incorporate all the perspectives into account individually.
- At first instance, one might wonder why physical evidences are classified; the following points will provide the answer: The class or type of evidence can be very important in determining its value
- How has it to be collected?
- What else needs to be collected along such as control samples and exemplars?
- And the most important is what sort of scientific tests should be conducted to draw varied conclusions from them?
Legal distinctions among different types of evidence help to determine their admissibility in the court of law. The following schemes to classify the physical evidences have been proposed by the scientists, which are comparatively more realistic than others:
- General nature of the physical evidence
- Type of material
- The physical state of the evidence
- The type of crime
- Classification on the way the evidence was produced, and
- Classification to the appropriate laboratory approach
General Nature of Physical evidence:
According to the overall nature of items, the physical evidences are often classified as physical, chemical, or biological (the biological are often associated to human, animal or vegetable). The examples of physical would be a paint, plastic, glass, firearm, cartridge case, tool, tool mark etc.
Examples of chemical evidences includes drugs, explosives etc.
Examples of Biological would include hair, pollen grains, and bloodstains DNA etc.
Type of Material
This classification system of evidence is based on the type of material of which it is composed of such as paint evidence, blood evidence, wood evidence, metallic evidence, glass evidence, plastic evidence, and paper evidence etc.
Paint evidence: any paint, liquid or dried, which will are transferred from the surface of one object to a different during the commission of the crime.
Glass evidence: any glass particle or fragment that may have been transferred on a person or object involved in a crime and window panes of buildings or vehicles containing holes made by bullet or other projectile.
The Physical State of the Evidence:
Evidences, like other matter, can be categorized on the basis of its physical state like solid, liquid, or gas.
Example of solid state category includes most types of evidence encountered cartridge case, firearms, glass, tools, clothing, and paper etc. Fewer items of evidence would be placed in the liquid or gas categories.
Important examples of liquid evidences include liquid blood samples (either evidence samples or known controls), alcohol and accelerants collected in connection with the investigation of suspected arson case.
Gas samples may occur as evidence more often than one might think, but they are rarely recognized as such and even more rarely collected. Specific types of devices can be used to collect sample of gases and vapors at crime and fire scenes.
Type of Crime:
Another system to classify the physical evidence is based on the type of crime from which it has been collected. Thus, for example, the evidences may be related to assaults, rape, homicide, burglary cases, and so on. This scheme might have value in certain situations, but it should be appreciated that any particular type of physical evidence can be found in connection with the investigation of virtually any kind of crime. Different physical evidence types cannot be restricted to legally defined crime classifications. For example, the blood/blood stain evidence very frequently found in the investigations of assault and homicide, but bloodstains can also be recovered as important evidence at crime scenes related to burglary and other property crimes also.
Classification on the Way Evidence Was Produced:
In this system of classification, the evidences are classified according to how it relates to the act under investigation. The way the individuals involved in the crime has interacted with the environment and with each other and the type of evidences produced during these interactions.
Physical evidences can be looked at as a type of surfaces (substrate or recording medium) on which they are present. Thus, in other words, the physical evidences are unintentional and somewhat imperfect record of the interactions of the perpetrator and victim, and with the environment.
Location/Geometric:
The apparent movement or disturbance of various objects is observed, documented and interpreted to reconstruct an event.
Imprints and Indentations:
Evidence in these categories includes tool marks in the form of indentations formed by tools, primer marks, breech face marks, pry marks; imprints like track marks formed by tire, gait pattern, fingerprints, footprints and bite marks. Class and individual characteristics of the suspected devices making the imprint or indentation are compared with the details of the specimen marks produced in the selected recording medium as specimens.
Striations:
Striations, another type of tool mark are produced when two surfaces come into sliding contact with each other. The marks resulted from a dynamic process are striations, in contrast to the static process, which results in the production of imprints and indentations.
Striations are marks consisting of numerous lands separated by grooves, randomly spaced, parallel streaks of varying length and width, Examples of striation mark evidence are produced as markings on bullets, marks made by certain cutting tools (machine tools, wire cutters, thread cutters, bolt cutters, knives, and axes), die marks on wires from the drawing operation, and extrusion marks on certain plastic and metal articles.
Striation marks can be produced in many varied situation where the surface of one object marks the surface of another because one of them is in motion relative to the other one. Some teeth marks/ bite marks, like those made in biting off a piece of cheese or fruit, for example. Striation markings possess both class and individual characteristics which may be useful within the process of identification and individualization.
Perforation Marks, Tears, Breaks, and Cuts:
This includes another sub-category of the evidence which is often of the greatest interest for potential individualization. Where, one or more pieces or fragments of an article are compared with other articles from which they are thought to have originated. If a sufficient number of individual characteristics are present then it become possible to conclude that the items share a common origin and were part of the same piece.
A glass fragment could be the best example to associate it with the particular window from which it was broken by fitting it into the area from which it originated. Such physical matches or jigsaw fits are applicable to a wide variety of other materials, including wood, cloth, metal, plastics, paper, and cordage etc. Sometimes, evidence such as paint chips can also fit into this category.
Perforation marks:
Another example of Physical fits is often the perforation marks punched during a receipt book to separate the counterfoil.
Breaks and tears normally provide the largest number of details for potential individualization, but success is sometimes possible in cases of cut pieces as well. In some of these cases, the individualization potential depends less on the nature of the cut, broken, or torn surface than on various features on, or within, the body of the article. Examples of such features include writing, printing, designs, surface topography, grain structure, pigmentation patterns, and characteristic irregularities.
Mutual Transfers of Matter:
In an accident case transfer of paint in the form of smear or chip evidence is result of contact between two surfaces and involves the mutual transfer of matter across the contact surface. Other evidences that can be included in this category are dusts particles, clothing fibers, vegetation, hairs, soil, pollens and small glass particles.
According to Locard’s principle mutual transfer of matter always occurs when two surfaces come into contact, but the amount of material transferred in some circumstances may be in traces and is practically not significant.
Deposits and Residues:
In this category the matter is transferred without any contact between the surfaces from where that matter originated and the surface on which it is transferred. GSR gunshot residues, explosive residues, fallen hairs, blood, glass fragments, oil drippings, and airborne particles are examples of this category. Such evidence may possess both class and individual characteristics and play important role in reconstructions of an event.
Classification According to the Appropriate Laboratory Approach:
All the sample which are referred to the laboratory must accompanied by the list of query related to the examination in the lab. In this scheme, the evidence can be categorized on the basis of the type of the following examination required:
- Identification
- Individualization
- Reconstruction
The evidence is examined which has relevancy to the investigation.
Identification
This process is depends on the class characteristics of the physical evidences. In some cases, only identification of a certain physical-evidence item is required. But individualization and reconstructions may become necessary in other cases to prove the charge of possession of a prohibited substance. The laboratory tests wont to establish a component of the crime. Criteria for the identification of physical evidence include morphological, physical, and chemical properties. However, combinations of some of these properties can provide useful information in achieving individualization also.
Individualization
After Identification of the material with class characteristics, Individualization is attempted supported on the individual characteristics of the physical evidence like fingerprints, broken glass, tool marks, paint chip and markings on bullets etc. The direct physical comparisons and physical matches (jigsaw fits) techniques can also yield persuasive individualizations under favorable circumstances.
Reconstruction
Reconstruction may be a final step of any criminal investigation. It refers to the process of putting together the “pieces” of a case or situation with the objective to reach an understanding of a sequence of past events. It can be achieved on the basis of physical evidence that has resulted from the events. Reconstructions are regularly desired in criminal cases where bloodstains or blood spattering patterns, gunshot residue patterns, shotgun pellet patterns, and relatively large fragments of broken glass are involved. Similarly, relationships among several other items of physical evidence can play useful role in reconstruction.
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