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Anatomy of Bullets
Anatomy of Weapons
Bite Mark Identification
Bullet Wound Analysis
Counterfeiting Methods and Detection
Document Tampering, Forgery and Ink Analysis
Drug & Poison Analysis of Hair
Footprints, Tool and Tire Mark Identification
Gun Powder Residue
Ion Mobility Spectrometry
Lipstick and Cosmetic Analysis
Molding Materials for Snow, Sand, Mud
Neutron Activation Analysis
Physics of Ballistics
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Footprints, Tool and Tire Mark Identification
Footprints, Tool and Tire Mark Identification
TIRE MARKS IDENTIFICATION
Tire marks are impressions in surfaces upon which a vehicle has driven on. However, depending on the surface and type of tires that are involved, determines the type of print that will be made. Some tires and surfaces will not even leave a print. Surfaces that are “softer,” such as snow or mud, will leave an imprint under the weight of the vehicle. On hard surfaces, tire marks are only made if dust or dirt was present.
Tires are made from a variety of different types of semi- hard rubber. These tires are classified by both class and individual characteristics. Depending on the surface that the vehicle had driven on, these characteristics will show up when analyzing the tire marks.
In forensic science, tire marks are extremely important. The two most frequent cases that involve tire mark investigation are tire marks found at scenes dealing with car accidents, in addition to scenes using vehicles to create escape routes. When tire marks are found at or near a scene, the first thing one will do is observe and record the marks. In order to do this, pictures of the marks will be taken at a 90-degree angle. This allows the class and individual characteristics to be analyzed. Next, the tire mark’s width needs to be measured, along with the circumference, if there is enough width to do so. Lastly, if the tracks are marked in “relief,” a cast is taken, usually using plaster of Paris. After this process is finished, a database of tires is consulted to determine the brand and model of the tire used in the scene. If the vehicle’s dimensions are known, it is easier to decide which vehicle left the tire marks. Using Locard’s Exchange Principle, if skid marks are left behind at the scene of the crime, investigators can collect these traces and can compare them with tires of an alleged vehicle.
This method of identifying tire marks was first created in 1930 by David Chapman, a researcher associated with the Sheriff’s Office in Los Angeles, California.
In 2002, in Wilson v. Cockrell, a Texan defendant was convicted of murder and sentenced to death. The Court of Appeals agreed that the evidence clearly supported the defendant’s conviction. Concerning the tire impression evidence, the court took note that the defendant acknowledged that they drove a car with two different types of tires, “tires that matched the tire tracks on the victim’s body,” and had “a large amount of human hair on its inner cartridge.” An expert witness testified that they could not exactly match up the two, but the hair found in the cartridge could definitely able to belong to the victim. Also, the tire marks on the victim’s body was from two different types of tires.
In 2004, in State v. Hernandez, the victim was murdered in a robbery by being brutally stabbed, and then ran over with a vehicle. Due to the strong connection of the death, Hernandez was charged and convicted for first degree murder and use of a deadly weapon to commit a felony. When investigators went to Hernandez’s residence, they spotted a vehicle with tires that were parallel to the tire tread taken from the victim’s pants. In addition, the investigators observed small, thick tissue type substances splattered on the undercarriage of the tire. They concluded this to be blood and bodily tissue.
In crime scene investigation, shoes can create impressions that are very informative for the forensic investigator. The soles of shoes pick up various materials when a person walks on them, which can easily transfer onto other surfaces that the person comes in contact with. The impression will give away what the pattern of the sole looked like. In detecting shoeprints, investigators look at soil, carpet, linoleum, paper, and dust.
The three types of shoeprints are plastic, patent, and latent. Plastic shoeprints occur when a shoe sinks into a soft substance such as snow or mud. Patent shoeprints are the most visible of the three and are created from tracking through a substance like dirt or paint, leaving a print behind in each step taken. Latent shoeprints are not visible. They are left on hard surfaces, such as glass or concrete.
When a footprint is discovered in a crime scene, it is always photographed. There are various techniques of collecting shoeprints, but the most common includes dusting with special powders, electrostatic lifting, and making plaster casts. After this step is finished, the pattern is taken back to the lab, and there the investigator can link the pattern to a specific manufacturer and type. There is also a shoe database that an investigator can use in determining the origin of a shoe. In addition, if the size of the sole is determined in the investigation, the size of the shoe can also be, leading to an increased knowledge of the physical profile of a perpetrator.
A shoeprint can also show an individual’s way of walking, clearly determined in the impact on the way their shoes wear-down. Also, sometimes it is possible to decipher if the perpetrator has a limp or any foot deformities. As one walks, the soles of their shoes come in contact with tiny cuts, scratches, and abrasions. No two people will have the same tread over a period of time, which leads investigators to more evidence.
Many times, an investigator will want to compare a shoe to a shoeprint found at a crime scene investigation. To do this, the investigator needs to create a print from the latter. To do this, you need to coat the shoe sole with a light oil, by pressing it into foam rubber impregnated with oil. Then, the shoe is pressed again paper, creating a print that will be visualized with magnetic powder. If a plastic print in needed for comparison, the shoe will be pressed into a similar surface that the original shoeprint was made in.
In 1992, in the People v. Campbell case, Illinois’ Supreme Court claimed “shoe-print evidence alone, is sufficient enough to convict.” Due to this, the defendant of this case clearly had the opportunity to commit the burglary, along with evidence of flight.
In the Ohio case of State v. Jells, in 1990, the Supreme Court permitted a police officer to testify in regards to the similarities in the defendant’s shoes and the prints.
A tool mark is simply an impression left by the impact of a tool on a surface. When this happens, an indentation of the exact tool is created. The analysis process by an investigator is done to figure out what tool created the mark. This is a very important aspect of forensic investigations because tools are used in many criminal activities. Like tire marks, tool marks have individual and class characteristics. The class characteristics contain the type of impression, its overall shape, and its general dimensions. Class characteristics usually allow the investigator to determine what type of tool made the impression and how the mark was created. However, characteristics do not clearly show what exact tool made the mark.
The two types of tool marks are slipped and molded impressions. Slipped impressions are made when tools are dragged or slid across a surface. The resulting tool mark is a sequence of patterns running parallel to each other following the course of the drag. For example, keying a car. Molded impressions are the outcome of the contact of a tool onto a surface with no “lateral motion”. The resulting tool marks are a three-dimensional mold of the part of the tool that contacted the surface. For example, the leverage of a door using a pry bar. Many tool marks are both slipped and molded impressions.
The steps to fully examining a tool mark are as follows. First, the examiner measure, observe and describe the mark. Next, a thorough photograph will be taken of the tool mark. Then, a cast of a tool mark is created, usually with polymeric dental paste. The comparison process is only started when a tool is discovered and its class characteristics match the ones exhibited by the tool mark. Then the tool itself is observed and photographed. Next, comparison tool marks are created on a soft material so that no extra marks are created on the tool. To compare the two, a comparison microscope is used. If there is a congruity between the individual characteristics, the common origin between the incriminated tool mark and the tool is created.
In the Ramirez v. State Case, Florida’s Supreme Court’s conviction was reversed, due to a testimony from a tool mark expert witness who had identified a specific knife as the murder weapon, because of various specific comparison of markings in a piece of cartilage.
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"Toolmarks: World of Forensic Science." ENotes - Literature Study Guides, Lesson Plans, and More. Web. 02 Jan. 2011. <
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