A tire could transmit an impression over various surfaces such as snow dirt roads and shoulders, and other unpaved areas. Also, a tire could leave a grazing mark of its sidewall or tread against the shirt of a hit-and-run victim or produce a blunt force injury that leaves a contusion that replicates its tread pattern on the skin of the victim’s body. The examination of these impressions can place the perpetrator’s vehicle at the scene of the crime. These impressions need to be recovered properly and their location and relationship to the crime scene must be properly documented. tires impression and tire track evidence are often away from the center of the crime scene area and in less conspicuous locations. Tire evidence will only be found if the crime scene personnel have a constant awareness of its possible existence and make an aggressive effort to search, locate, document, and recover it. The first officer on the scene must take early action to protect the scene from other vehicular and pedestrian traffic. Along these lines, an officer responding to any crime scene where surface conditions would allow for the retention of tire impressions should immediately preserve that entire area in anticipation of the potential existence of this evidence. The investigator’s limited knowledge of tire evidence, including incorrect measurements of only the front tracks and, later an incorrect assessment and measurement of the perpetrator’s vehicle, rendered this evidence essentially useless.Where the total tire impression runs for 4 feet or less, the entirety of that impression can and must be recovered through both photography and casting. For scenes having multiple and/or longer impressions, the task of recovering all of the impression evidence soon becomes logistically impossible. Still, the recovery of a sizeable portion of this evidence in the proper way should be made to ensure each tire impression is represented and to significantly increase chances for identification with a tire from the perpetrator’s vehicle. Any track dimensional information present should also be carefully measured and documented. When trying to assess the value of tire impressions at a scene. This is compounded by the fact that often there are several sets of tire tracks and impressions and, in some cases, there may not be any preliminary information that might suggest which of these, if any, may have been made by the perpetrator’s vehicle. In general, the best guidelines regarding how much should be recovered can only be discussed in terms of the minimum amount, which should include photographic documentation and at least one 3-foot cast of each of the potentially important tracks. The recovery of tire evidence at any particular scene involves several particular procedures and techniques. If a tire will leave its impression on the victim’s clothing or on debris such as wood or paper that it tracked over, the original items bearing those impressions should always be recovered after photography and documentation at the scene. If a digital camera is used, it should minimally be an 8-l2-megapixel professional digital SLR camera. The use of identifiers positioned next to the impressions, and thus visible in the photographs, provides an easy and accurate way to link the crime scene written notes with the actual evidence that is later recovered through examination quality photography and casting. The technique of photographing from several sides and perspectives not only is a more effective way of documenting the tire impressions, but also takes advantage of the way natural light reflects off of the impressions from different angles. The term examination quality photograph refers to a photograph taken with the camera positioned directly over the top of the impression for the specific purpose of later using that photograph in a detailed examination with tires from a suspect vehicle. Because they are taken for the specific purpose of examination, each and every one of these photographs must include a linear scale such as a ruler. Examination quality photographs are being taken for one purpose only and that is for a detailed examination that is very reliant on accuracy in size. Any photograph not taken properly with a scale in the picture is of greatly diminished value.. One of the most important factors is recognizing and understanding the need to photographically record the impression in a way that will allow dimensionally accurate natural-sized enlargement to later be prepared. A very common mistake made when photographing impression evidence is the failure to position the ruler on the same plane as the bottom of the impression. When sinking the ruler down to that level of the bottom of the tire impression, position the ruler next to but not in the impression. The yardstick provides a straight and rigid 36-inch scale. A series of overlapping photographs must be taken for impressions greater than 12 to 14 inches. These photographs can later be spliced together to reconstruct the longer impression.3-dimensional impressions should always be cast. Casts provide very accurate representations of tire impressions and allow for the recovery of more detailed and size accurate evidence a three-dimensional cast represents the details of the impression better than a photograph. To make casts of tire impressions, the proper dental stone material and the proper technique are essential. If the impression is only 3 to 4 feet long, the entire impression can and should be cast in one single cast. In the case of longer impressions that logistically cannot be cast in one piece, anycast that is poured should be minimally 3 feet in length. Short casts that are produced with a 2-pound bag of dental stone are normally no greater than 6 to 8 inches in length. Dental stone is used worldwide to cast footwear and tire impression evidence. Because there are many forms and qualities of the dental stone, those using and ordering dental stone should be aware of some basic qualities such as the powder-to-water ratio and the compressive strength that are essential for casting impression evidence. The powder-to-water ratio is determined by the manufacturer for each product. This information is either printed on the box or included inside the box of dental stone purchased from a dental supplier. Another quality to be aware of is the compressive strength, measured in pounds per square inch (psi). Dental stones used for casting impressions should have a compressive strength of 8,000 psi or higher. The lower the consistency the higher its compressive strength will be. Knowing the consistency of the dental stone you are using allows you to figure out how much water is needed per Portion of powder. Preparing the mixture for casting is by estimating how many pounds of dental stone will be needed for a particular impression based on the length, width, and depth of the impression to be cast and then calculate how much water is needed for that quantity. Pouring a bucket full of dental stone directly onto the surface of the impression can easily destroy it if proper precautions are not taken. With some impressions, the natural topography around the impression may permit pouring the dental stone on one side of the impression and allowing it to flow naturally into the impression. All casts should be labeled appropriately before they are removed from the ground. More commonly, those preparing the cast have traditionally scratched their initials and other information onto the back of the cast. Prior to lifting tire casts, the casts should always be photographed to show their relative positions at the scene. It is permissible and recommended, when lifting the cast from the ground, to use fingers to rub away the excess soil or sand, as this will only help the cast dry and make it easier to handle.48 hours are generally necessary for the excess water within the cast to move to the surface and evaporate. Once dried and hardened, casts made in some soils require little more than a controlled rinse and perhaps a light brushing with a wet brush. The recovery of a tire impression in the snow like on other surfaces must begin with good documentation and general scene photograph eventually followed with examination quality photograph and casts. One technique that helps provide contrast is a careful application of a snow wax or colored spray paint applied at a 45-degree angle so that it grazes the ridges or high areas of the impression. Short bursts of spray seem to be easier to control while doing this and help avoid any damage to the impression from the force of the aerosol. The impression should be photographed immediately after colorizing it and/ or the impression should be protected from the sun in some way from the moment it is colorized. The dry-casting method, which is the easiest and best overall method available for casting most impressions in snow. With only two additional items, a flour sifter, and a spray bottle, along with dental stone, a very good cast can be easily made of impression in the snow in a short time. Colder temperatures will require more time for the dental stone to harden. Extremely cold temperatures require a small amount of potassium sulfate added to the water source when mixing the cast. The application of an aerosol snow wax followed with dental stone can also be used to successfully cast impressions in snow. Sulfur has always been one of the better methods to cast snow impressions, although there is added time involved. Nevertheless, for those highly detailed dry snow impressions, the best chance of recovering the finest detail will be with sulfur.Tire tracks at a crime scene are a form of pattern evidence that can be documented, collected, preserved, and evaluated by a forensic footwear or tire tread examiner. Through scientific examination, comparison, and analysis, the examiner can use footwear and tire track evidence to clear the innocent, track down the guilty, and help the prosecution gain a conviction in court. Final results of a footwear/tire track examination are presented in a report that states the opinion of the examiner. It conveys the examiner’s observations and conclusions to the person or agency that requested the examination and to the court. It may also include additional statements concerning the likelihood that the shoe or tire made or did not make the questioned impression, supporting the examiner’s determination. can you make it simple and shorter! I Want to be 2 pages only!
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