How do you properly collect evidence without contaminating it

A successful crime investigation is much dependent upon the collection and analysis of different types of evidence. Investigators and forensic scientists categorize evidence in varied methods and adopt precise measures in dealing with them. A major difference in this regard is the classification of physical and biological evidence and both have to be handled with utmost care by investigators so as to prevent them from getting contaminated. Although some kinds of physical evidence are collected quite easily, caution has to be exercised so that they are not contaminated by way of for example, leaving finger prints on them. Packaging methods have to be used as per the nature of the evidence.

In essence, evidence has to be handled with care because eventually it will be used in proving a crime in a court of law. This paper will examine the different kinds of procedures that must be adopted in avoiding contamination of evidence.

Criminalists have to collect physical evidence from the scene of crime and it is extremely important to collect such evidence with utmost caution in order to prevent its contamination and destruction. It is important to ensure safe delivery of the evidence to the laboratory because it is here that the evidence is examined and analyzed for further applicability in judicial processes. Proper care of evidence is essential since it has to be presented in court in providing professional testimony about the establishment of the crime and the methods that have been used in ascertaining the findings.

Crimanalists are expected to have important skills, knowledge, and abilities in carrying out the work of collecting evidence from the scene of crime. They must know how to gather and organize information have skills of reading comprehension, problem identification, critical thinking and adequate knowledge of chemistry. A well organized procedure has to be adopted in collecting pertinent evidence so that it is not destroyed or contaminated.
Physical evidence is extremely important in establishing the different aspects of the crime and in identifying or eliminating suspects. It can also be used in corroborating or disputing statements made by principals. In criminal cases, the encountered evidence mostly pertains to biological evidence such as semen, fingerprints, impression evidence such as shoe prints and trace evidence such as hair and fibers. Different items have to be handled differently while dealing with evidence so that they are not contaminated or destroyed. Blood that is found at the site of the crime in pools of liquid should be soaked into a gauze pad or other clean and sterile cotton cloth and allowed to dry thoroughly at room temperature. In order to prevent its properties from getting contaminated it must be stored in a refrigerator or frozen immediately and sent to the laboratory at the earliest. Delays exceeding two days can render the samples without any use. If the criminalist is close to the laboratory the stained items should be delivered immediately, otherwise it should be mailed after allowing the stains to dry completely before it is packed. Stained material should not be heated or placed in direct sunlight and stained clothing that is collected as evidence must be hung in a room that is adequately ventilated. If the item is not entirely dry and has to be sent immediately for specific reasons it should placed in a brown paper bag and sealed after labeling its container. Only one item should be put into each container but plastic containers should not be used (Forest, 1983).
In regard to autopsy blood samples, the pathologist should take the blood from the heart directly and put into a yellow or purple colored stopperred vacuum container. When no blood is available in the body the pathologist should be asked to collect sections of the liver and bones or deep muscle tissues. All items at the scene of crime that have any evidentiary value should be collected. Photos should be taken of the scene and the items of evidence and sketches made to establish spatial relationships. Biological evidence in the form of hair, blood, semen, saliva and other body fluid stains can form vital evidence during investigations. In the case of rape the bedding on which the assault had occurred should be collected and all wet stains on it should be located and indicated with a tape. After allowing the bedding to dry it should be packed by folding along the edges and then placed in a paper bag. All other items that have any evidentiary value must be collected in terms of items that were in contact with the assailant or those that give indication of originating from the victim, such as clothes (Physical Evidence Bulletin, 2002).
Biological evidence is prone to deteriorate and one must be careful in collecting and storing such evidence so as to gather important information from its analysis. Blood stains are known to provide important clues, which imply that blood stain patterns must be documented with relevant sketches and photos. Biological evidence also contains infectious organisms which can be transmitted to anybody coming in contact with it. Hence proper safeguard and preventive measures have to be adopted. Care should be taken so that such evidence is not contaminated during the collection process. Any particular piece of biological evidence should not be allowed to come in contact with other samples. All stains should be handled separately and any two items should never be packed together. A sample should not be allowed to come in contact with a surface area that had contained residues of another biological sample. In this context, blood stained gloves previously used tweezers etc should be kept away from new samples. All implements such as tweezers and scissors should be cleaned with clear water and dried thoroughly with a drying agent before using them on another sample (Siegel, 2007).
Poor packing of evidence can have severe consequences on any investigation. Since the evidence is admissible in a court of law it is important that it is not compromised or contaminated or else the value of the evidence will be reduced. Whatever be the shape or size of the items, they must be packed in following the standards and principles of recovery so that integrity and continuity is adhered to and cross contamination is avoided. Sharp items should be properly packed in strong containers. In keeping with integrity of service all items should be appropriately packed at the scene of crime itself and packing material must be used only once. Items may be required to be stored for long periods and should therefore not be packed in bulky boxes and as far as possible, plastic bags should be used. Paper bags should not be used for items that are wet, but are good for most dry items since they allow the items to breathe. They should always be used for dry footwear and clothing. Paper bags should always be sealed at the seams to ensure the integrity of evidence (Bachman, 2007).
Cardboard boxes are useful for packing glass samples and sharp objects but items should be taped or tied in the inside of the cardboard box so as to prevent it from moving. It must be sealed around the edges and openings in order to ensure integrity. Plastic bags are convenient packing material and can be used for items that do not have any moisture, although they should never be used for sharp objects.

Knife tubes are rigid plastic tubes that have to be used for H  F reasons. They have a telescopic design and can fit varied sizes. They should be sealed correctly along with attached exhibit labels. Nylon bags should be used for evidence that is collected at fire scenes. The nylon bag must be allowed to contain some air and then sealed with a swan neck. Beechams wrap is a paper fold that is used to pack trace evidence. It must be sealed properly in order to avoid contamination of evidence. It needs to be placed inside a bag and nothing should be written on it.


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