1. Impressions and Tool marks Chapters 15 & 16 PVMHS, 2015

2. Student objectives:  Distinguish between patent, latent, and plastic impressions  Describe how to make foot, shoe, and tire impressions  Use track width and wheel base information to identify vehicles  Prepare dental impressions and match them with bite marks  Describe the three major types of tool mark impressions  Summarize the steps of a tool mark examination and analysis  Match tool marks with the instrument that produced them of 40 2

3. Labs & activities:  Casting a shoe impression  Examining the relationship between height, gait, & shoe size  Examining tires  Compare and contrast tire tread  Find the match  Examination of bite marks  Case study of Alampi/Bevard hit- and-run  Study of OJ Simpson case of 40 3

4. PART I Impressions Chapter 15 of 40 4

5. Types of impressions:  3 basic categories:  Patent – visible 2 dimensional impressions produced as an object moves through soil, dust, paint, blood, or other fine particles.  Latent – hidden to the eye, but can be discovered by dusting or applying chemiluminescence materials. Oils, dirt, dust, or other fine particulates can be transferred to a floor or wall and leave a latent impression.  Plastic – visible 3 dimensional impressions left in soft materials such as snow, mud, soil, or soap. Plastic prints are easily lost, therefore they need to be photographed immediately and then a cast should be taken. Cast of shoe impression Tire impression – plastic Latent shoe impression of 40 5

6. Individual vs. Class evidence  Depending on the impression, it can be categorized as either individual or class evidence.  Class evidence: a particular tread pattern may identify a specific brand of shoe or tire, but it will not identify an individual.  Individual evidence: if distinguishing characteristics are identified, such as unusual wear on a tire or a “scar” on a shoe, can be used as individual evidence. of 40 6

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8. Shoe impressions  There is a lot of information that can be ascertained from a shoe impression:  Shoe size  Weight (plastic impression)  Type of shoe gives information about the suspects job, personality, income, gender.  Gait  Approximate height  Databases exist to aid investigators in researching a tread pattern.  Ex: SoleMate, SICAR6 of 40 8

9. Shoe wear patterns  If two people purchase the same shoes on the same day, over time the tread will change even though it matched at the start.  This is because different people have habits of walking as well as different styles of walking.  Some people walk with more pressure on their toes, heels, outside of foot, inside of foot.  Some people may have a high arch or a flat foot  Some people walk with toes straight, others with toes pointing out, or in.  Some people have narrow feet, others are wide.  Etc. of 40 9

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12. Gait & Tracks  If there are several footprints together, it may be possible to determine the suspect’s gait.  If a person has a limp or is carrying something heavy, it may cause an asymmetrical gait – i.e. one foot is angled differently from the other or one impression is deeper than the other.  Tracks can indicate if a person was running or walking based on the length of stride, shape of impression, and pressure points on the impression.  Tracks can also indicate movements and even pinpoint the order that the movements occurred in. of 40 12

13. Collecting shoe impression evidence  #1!!! Photograph  Impressions should not be touched or tampered with in any way until they are photographed.  Photograph all impressions right away, regardless of the type of impression found.  Take additional photos with a ruler in position.  #2 – lift or cast the impression  2 dimensional impressions can be lifted using luminol or dusting  Casts can be made of 3 dimensional impressions and preserved to be used as physical evidence.  Casting impressions in snow can be accomplished using a special spray wax and a material called dental stone. of 40 13

14. Foot length & shoe size  It’s impossible to predict an individuals exact height from their shoe size.  It’s important to remember that a shoe print provides some information about the person who left it but:  The size of shoe varies by brand/type  The suspect may be wearing shoes that are not appropriately sized. of 40 14

15. Shoe size & height of 40 15

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17. Tire tread and impressions  Tire marks can be used to identify a vehicle at the scene of a crime.  Tire marks can indicate the speed and direction a vehicle traveled.  Skid marks at an accident scene may indicate who was at fault or help reconstruct what happened.  Forensic scientists examine tire tread and impression for 2 reasons:  Tread pattern and measurements can identify the type of tire and potentially the make and model of the vehicle,  The impression can determine how the car was driven (speed, direction, etc.) of 40 17

18. Tire tread and impressions  Vehicles can leave 3 types of impressions:  Patent impressions occur after a vehicle has driven through a fluid material like tar, oil, or blood.  Latent marks may be left on asphalt or concrete roads by oils in the tire that are meant to keep the tire soft and pliable.  Plastic impressions may occur in off road surfaces like mud, snow, or sand. of 40 18

19. Anatomy of a tire  A tires surface is divided into ridges and grooves.  Ridges are the elevated regions  Grooves are the indentations  The purpose of this design is to channel water away and provide traction with the ground.  Every model of tire is unique.  Width and angle of the grooves are uniquely engineered for each model.  Touring tires have small grooves to channel air and water on smooth pavement.  Off road tires have wide deep grooves to provide traction in slippery conditions. of 40 19

20. Anatomy of a tire  Tread patterns are symmetrical, with the left and right sides as mirror images.  Ribs (the ridge of the tire) and grooves are counted across the entire tread width from shoulder to shoulder.  If the tire has a central ridge, it will have an uneven numbers of ribs.  Wear patterns and other imperfections should be noted.  To match the tire pattern of a suspects car to an impression taken at the crime scene, at least 3 meters of tire mark must be obtained as a sample from the suspect vehicle.  Done by inking the tire and driving it onto paper. of 40 20

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22. Identifying a vehicle  Because the same type of tire may be used on many vehicles, just identifying tread pattern often isn’t enough.  Track width and wheelbase will also need to be measured.  Track width is measured in mm from the center of each tire to the center of the opposite tire.  Wheelbase is measured in mm from the center of the front axle to the center of the rear axle. Wheelbase Track width of 40 22

23. Identifying a vehicle  Turning diameter is the measure of how tight a circle a vehicle can make.  A longer wheelbase increases the turning diameter.  There is a large database that contains the track width, wheelbase, and turning diameter for all makes and models of cars.  This information can be accessed to identify the vehicle that left an impression.

24. Accident reconstruction Establishing car movements from tire marks  A vehicle’s direction of travel can be established by studying:  Vegetation disturbed by the vehicle.  Patterns of debris cast off by a moving vehicle.  Splash patterns created as a vehicle moves from wet to dry pavement.  Substance transfer, such as oil leakage, from vehicle to pavement.  Tire marks  Photographs and measurements are recorded to reconstruct the events of an accident.  The goal of accident reconstruction is to determine what happened. of 40 24

25. Hit-and-run  In hit-and-run situations, the vehicle is gone but tire marks, splash patterns, pattern of debris, and substance transfer can all be used to determine:  Speed and direction of movement  Whether brakes were applied or not  Whether the vehicle accelerated to “get away” from the scene  Case study: Alampi/Bevard case of 40 25

26. Tire marks  There are three basic types of tire marks.  Skid marks  Yaw marks  Tire scrubs of 40 26

27. Skid marks  Formed when someone brakes suddenly  Provides evidence of the point at which the brakes were applied.  Calculation of velocity can be made from skid marks. of 40 27

28. Yaw marks  Produced when a vehicle skids sideways due to traveling too fast as it turns.  Tires and the road surface melt from extreme temperatures (friction).  Audible squeal and smoke. of 40 28

29. Tire scrubs  Produced by damaged or overloaded tires during or immediately following an accident.  Usually appear curved, irregular in width.  May have striations that look like stripes.  Can be used to determine area of impact. of 40 29

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31. Dental impressions  Bite marks are considered individual evidence.  Factors that contribute to individuality:  Number  Size  Alignment  Dental work of 40 31

32. Dental impressions  The individuality of teeth can be used in forensics two ways:  To identify remains  To implicate a suspect in a crime  Up to 76 points of comparison may be used when comparing bite marks, including:  Chipping  Surface indentations/grooves  Tooth dimensions  Distances between teeth  Alignment of teeth  Angle of mouth arch  Missing teeth  Dental work of 40 32

33. Processing a bite mark  Gloves should be worn when touching a bite mark.  Bite marks should be photographed immediately  A ruler should be included for reference  Bite marks should be swabbed for saliva.  Bite marks descriptions should be recorded in a report.  A forensic odontologist should be consulted  Bite mark photographs should be scanned photographic distortion corrected.  Dental molds should be taken from any suspects. of 40 33

34. Part II Tool Marks Chapter 16 of 40 34

35. Tools and crime scenes  Some of the most common type of physical evidence left at a crime scene are tools.  Tools generally have unique characteristics, even though they are manufactured in bulk.  There are 3 categories of tool marks:  Indentation marks  Abrasion marks  Cutting marks  Photographs should always be taken of tool marks when processing a crime scene. of 40 35

36. Indentation marks  Indentation marks occur when a tool is pressed into a softer surface.  The impression can be measure to determine size and shape of the tool. of 40 36

37. Abrasion marks  Made when surfaces slide across one another.  Pliers, axes, knives, and gun barrels are just some of the tools that make this type of mark.  Some indentation marks and abrasion marks are made at the same time, such as by a pry bar forcing a door open. of 40 37

38. Cutting marks  Cutting marks are produced along the edge as a surface is cut.  Saws & wire cutters leave cutting marks.  By examining the cut surface of a bone, it’s possible to determine the type of saw blade used. of 40 38

39. Tool mark examination  Always document with a photograph, a ruler should be included in photo for reference.  Tool mark evidence can be removed from the scene to preserve it.  Investigator may actually cut a section out of a door for this purpose.  A cast can be made using a rubber-based casting material if the evidence can’t be removed.  Always dust for fingerprints first.  Always wear gloves.  Evidence collected should be wrapped in paper and labeled or placed in a box so that it does not become damaged. of 40 39

40. of 40 40 Any questions? THE END