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Impressions Evidence Coach Whitaker. Vocabulary Impression evidence—objects or materials that have retained the characteristics of other objects through.

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Presentation on theme: "Impressions Evidence Coach Whitaker. Vocabulary Impression evidence—objects or materials that have retained the characteristics of other objects through."— Presentation transcript:

1 Impressions Evidence Coach Whitaker

2 Vocabulary Impression evidence—objects or materials that have retained the characteristics of other objects through direct contact Handguns—are held and fired in the hand three categories of handguns Revolvers—cylinder fired handgun Semi-automatic—loaded using a magazine or clip

3 Vocabulary Machine pistol—automatic pistols Rifles—use lever or sliding bolt to eject a spent cartridge—semi or auto—shoulder Shotguns—fires shells with groups of pellets

4 Vocabulary Lead bullets—are soft and found in low-velocity weapons (22’s)—bullets deform easily—less penetration Lead alloy bullets—contain metals that are much harder—high velocity weapons—deform less and penetrate more Semijacketed bullets—have a thin layer of brass that coats the bullet with a soft lead nose that allows for good penetration with expansion Fully jacketed—are fully brass and are known as cop killers

5 Vocabulary Caliber—is a measurement in inches of the internal diameter of its barrel Entry wound—is where a bullet enters the body Exit wound—is where a bullet exits the body—just because there is an entry wound does not mean there is an exit wound

6 Impression evidence can be defined as objects or materials that have retained the characteristics of other objects through direct contact. Impressions are created when one object is pressed against another material with enough force to leave an impression of the object. Shoeprints, tool marks, tire tracks, bite marks, and marks on a fired bullet are several examples of impression evidence. Impressions may be found in or on many different types of materials. The quality of the impression depends on the object making the impression and the surface conditions, such as how hard or soft it is and what type of material it is (soil, mud, dust, concrete, grass, skin, etc.) Images: and CSI & Impressions What is impression evidence?

7 Collection Methods Investigators analyze the impression evidence to find unique characteristics to link shoes, tires, tools, and other objects found in a suspect’s possession to evidence at a crime scene. Collection of impression evidence can be accomplished using several methods: 2-D: This type of impression is documented using photography. Some impressions may be dusted with fingerprint powder to be photographed or lifted with tape. They may also be collected using an electrostatic dust lifting process. 3-D: This type of impression can be documented using photography as well as by casting, which involves using dental stone or a similar substance to preserve the dimensional characteristics of the print. Images: Example of Shoe Print in Bio-Foam Impression Foam

8 Tire tracks are important in forensic investigations and are usually found in road accident scenes or in the access and escape routes of other crime scenes. Tracks help investigators identify the type of vehicle that left them. Investigators may make ink prints of a tire or plaster casts of a track. They will also take photographs that can later be used to prove a match. Features to analyze: Tread pattern Width & depth of the tread pattern Unique characteristics due to the wear pattern or defects Images: Tire Track Evidence Tire databases are available help investigators determine the brand and model of the tire that left the impression, which can be used to determine the type of vehicle that made the tracks.

9 Certain defects or patterns may be left on a tool when it is made or used, which can be used to find matches between evidence at a crime scene and tools or objects found at a suspect’s home. Images: and Features to analyze: Dimensions of the impression Ridges or striation patterns Defects, such as nicks and chips Paint chips or metal shards left on a tool Tool marks can be classified two ways: (1)Impressions – As a tool hits a softer surface, the shape of the tool and imperfections in its surface may be left behind as an impression. (2)Scratches – As a tool moves across a surface, it may leave ridges or striations behind. NOTE: Some tool marks are a combination of both types. Tool Mark Evidence

10 Investigators can analyze a shoe print to determine its class, or the type and brand of shoe. They will also look for individual characteristics, such as wear patterns and specific damages or defects. Databases of shoe prints are available for investigators to help them determine the brand of shoe to provide leads for a case. Depending on the quality of the impression, investigators may be able to determine a person’s speed (walking vs. running) as well as estimate the size of a person based on the impression’s depth. Features to analyze: Tread patterns, size, and depth Wear patterns caused by the way a person walks Material defects or damage (nicks, cuts, etc.) Other trace materials, such as soil, tar, rocks, and paint that would indicate where a person has been Images: and Shoe Print Evidence Shoe Print in Bio-Foam Impression Foam STAMP Database

11 Did you know? The most famous incident where bite mark evidence led to a conviction, was in the case of the notorious serial killer, Ted Bundy. He was responsible for an undetermined number of murders between 1973 and 1978 and was finally tied to the murder of Lisa Levy through bites that he had inflicted on her body. Investigators can analyze bite marks for characteristics to help them identify victims or suspects as well as to exclude others. Marks can be left on a victim’s skin or other objects, such as Styrofoam cups, gum, or foods. Saliva or blood may be left behind that can be tested for DNA. Dental records including x-rays can also provide useful information, especially when attempting to identify a victim. Features to analyze: Type of bite mark (human or animal) Characteristics of the teeth (position, evidence of dental work, wear patterns, etc.) Color of area to estimate how long ago the bite occurred (old or recent bite) Swab for body fluids for DNA tests Images: Bite Mark Evidence Bite Mark Evidence Video

12 Impression Impressions Scavenger hunt Looking for eight different impressions evidence Photograph and write where it was from and other information on your handout

13 Forensic Science Activity T. Trimpe 2007

14 Tool Marks Lab Goal: Your group will need to examine and document the tool marks made by each of the tools. At each station, you will need to: 1 – To prepare for the lab, roll the modeling clay into a flat circle that fits inside the plastic plate. Make several impressions of each tool in your slab of modeling clay. 2 – Use the ruler to record the measurements for each tool and its impression surfaces. 3 – Document any unique characteristics you notice on each tool or its impression. Write your observations on your worksheet. 4 – After you have documents both of the tools at that station, roll the clay into a ball to prepare for the next group and wait until it's time to rotate to the next station. Features to analyze: Dimensions of the impression Ridges or striation patterns Defects, such as nicks and chips Paint chips or metal shards left on a tool Image:

15 Work with your investigative team to identify the crime scene tools. Compare the tool marks you made earlier and match them to the crime scene tools. Once you have identified all the tools, have your answers checked by your teacher. Keep trying until you have them all correct! Tool Mark Challenge

16 Going Ballistic

17 Forensic Firearms Examiners Analyze bullets and shell casings found at crime scenes to determine the type of gun Help with crime scene reconstruction by estimating the distance between the gun muzzle and victim Match a bullet or shell casing to a particular gun

18 Types of Guns Handguns—are held and fired in the hand Three categories of handguns Revolvers—cylinder Semi-automatic—loaded using a magazine or clip Machine pistol—automatic pistols Rifles—use lever or sliding bolt to eject a spent cartridge—semi or auto—shoulder Shotguns—fires shells with groups of pellets

19 Ammo Evidence When collecting bullets, great care must be made because: A bullet may be altered or damaged A bullet may have important trace evidence attached to it A bullet may have DNA on it *fragments of bullets are most often collected*

20 Ammo Evidence Lead bullets—are soft and found in low-velocity weapons (22’s)—bullets deform easily—less penetration Lead alloy bullets—contain metals that are much harder—high velocity weapons—deform less and penetrate more Semijacketed bullets—have a thin layer of brass that coats the bullet with a soft lead nose that allows for good penetration with expansion Fully jacketed—are fully brass and are known as cop killers

21 Determining Caliber and Gauge The caliber of a handgun or rifle is a measurement in inches of the internal diameter of its barrel Shotgun gauges are determined by counting the number of lead balls matching the barrel’s diameter that it takes to weight one pound The caliber and type of bullet is important in determining what type of gun was used in a crime

22 Shell Casings Is the portion of the cartridge that remains after the powder explodes and the bullet is gone The retain many marks including: 1. The impression used by the firing pin—helps to narrow down the list of possible gun types 2. Breechlock patterns—is the back wall of the firing chamber—impression is made on the bottom of the casing 3. Headstamp—bullet makers have their stamp and caliber and gauge 4. Extractor and ejector marks—leaves their own unique scratches and marks on the casings

23 Gunshot residue When a gun is fired, the explosion between the primer and powder creates a residue that cling to the shooter’s hand, arm, clothing, face, and hair

24 Activity Out of ten bullets, you tell the caliber, type of gun, bullet, and find two guns that could fire that particular bullet lab

25 Tracing Tricky Bullets When bullets enter the body there is no telling where it will end up Entry wound—is where a bullet enters the body Exit wound—is where a bullet exits the body—just because there is an entry wound does not mean there is an exit wound Examiners try to trace the path of a bullet through a body

26 Character of Wounds The type of wound produced by a gunshot depends on several factors including: The distance between the victim and the gun muzzle The caliber and velocity of the bullet The angle at which the bullet enters Whether the bullet remains or exits the body

27 Determining Distance The ME can estimate the distance from which a single bullet was fired by looking at the entry wound If the muzzle was 2 or more feet away, the entry wound is usually a small hole with an abrasion collar If the muzzle was 6 inches to 2 ft, the skin may appear to be tattooed or stippled If the muzzle was less than 6 inches, the gunshot produces a hole, a compact area of stripling, a surrounding area of charring, and a bright red hue to the wounded tissue If the muzzle is pressed against the victim, hot gases and particles are driven directly on the skin and creates a star shaped pattern

28 Exit Wounds Exit wounds are typically larger than entry wounds because the bullet lacerates the tissues as it forces its way up and out the skin Depends on the size, speed, and shape of the bullet Sometimes entry wounds contain materials or clothing in the wound

29 Shotgun Patterns A shotgun shoots a group of pellets or shot and creates multiple entry wounds The closer a victim is the smaller the pattern and the further away a person is the more the pattern is spread out Shot—multiple pellets Slug—one piece of lead

30 Activity AL/GUNS/GUNINJ.html AL/GUNS/GUNINJ.html Gunshot drawings of different wounds

31 Activity racksinfo.pdf racksinfo.pdf Tire Tracks Challenge


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