- Slides: 43
Tool Marks and Other Impressions
Tools in Crime • • • • Locking Pliers Needle Nose Locking Pliers Slip Joint Pliers Tongue and Groove Pliers Linemans Pliers Diagonal Cutters Wire Cutters/Strippers Pipe Wrenches Circular Cutting Tools Chisels Screwdrivers Pry Bars Bolt Cutters A-Rods Hammers
Tool Marks • Any cut, gouge or abrasion caused by a tool • Tool leaves striations on softer surface that match marks on the surface of the tool • 3 Types of Marks • - Indentation - negative impression of object in softer surface (screwdriver) • - Abrasion - made when 2 objects slide past each other (gun barrel/knives) • - Cutting - produced along edge when surface is cut (saws/wire cutters)
Tool Marks • Indented Impressions – What can we determine? • Size (class) • Shape (class) • Random nicks and breaks in tool (Individual)
Class characteristics to look for in different tools: • Pliers: - opposing jaws which grasp onto an object.
Screwdrivers • Designed to impart torque on a screw - may be used as pry tools by criminals. • Class characteristics of screwdrivers include: - Blade width - Blade thickness - Surface texture
Prybars • used to gain leverage between two objects. • slots in each end ensure a solid grasp on a smaller items Class characteristics include: • Blade width • Blade thickness • Space between the blade tips
Chisels • bladed tools designed to compress material when struck. • The bevel is the angled area from the tip to the blade face. • Class characteristics: – Blade width – Blade thickness – Bevel thickness
Hammers • Claw hammers get their name from the split rear area of the hammer used to pull nails. • The class characteristics for a hammer include – hammer face diameter – claw width – claw space width – claw thickness
Connect Suspect Tool to Crime Scene • Make impressions using suspect tool at various pressures and angles in soft metal • Compare under comparative microscope
• Individual Characteristics • Unique marks are transferred to the objects they contact. • These are microscopic imperfections caused by: • The manufacturing process • Use • Abuse • Rust
Impressed Toolmarks / Indented Compressions / Compression Marks • Mirror images of the tool • All imperfections on tool surface transfer to the impression • Used for comparison and identification
Striation Marks • The tool is moved across an object (with pressure) producing a striated mark. • Screwdriver most often leaves these types of impressions - Criminals typically use screwdrivers to try to pry open cash drawers, windows, doors, and car locks.
Crime Scene Procedure • - NEVER stick suspected tool into crime scene impression! • - Many tool marks can not be removed from the crime scene - Measure and photograph all impressions - A cast must be made - Casting makes a negative impression of the toolmark - Typically done with Mikrosil, but many other options available - Mikrosil must be mixed prior to using. - After mixing, it is applied to the area of the toolmark.
• - Casting is documented and photos are taken • - Once Mikrosil is hard, peel from surface • - (Hard casts have other procedures) • - The casting is a mirror image, therefore a casting of suspected tool must also be made for comparison
Casting a Suspect's Tool - Make impressions using suspect tool at various pressures and angles in soft metal (lead) (Sometimes a cast is made of these impressions as well) - Measure and compare width/length (Class characteristics) - Look at striations under comparative microscope (individual characteristics)
Tool Marks Popped Steering Column Tool Marks
Tool Marks Suspect Screwdriver Scrap screwdriver into soft surface at various angles and pressure
Tool Marks Cast of steering column marks Compare to screwdriver cast marks
Shoe Impressions • What can we tell? – Shoe type – Shoe size – Show wear patterns
Wear Patterns - Toe or heal walker activity of wearer - Body Weight surface they walk on - Walk with feet inwards or outwards unique holes/cuts/debris in shoe -
What material can shoe impressions be left in?
Locating Shoe Prints Often found near: - The actual point of occurrence of the crime - The route through the points of entry/exit & the crime scene - Exterior areas
How common are Shoe Prints? Combination of floor surface and condition of footwear determines likelihood of a foot print.
Likelihood of a Shoe Print
Shoe Impressions • Can leave impressions in dust • Photograph • Electrostatic lift – Overlay dust with mylar film sheet
Shoe Impressions • Can leave impressions in soil • Photograph • Make a cast with dental stone
Shoe Impressions • Can leave shoeprint in snow • Photograph • Spray with 3 coats of Snow-Print Wax • Cast with Dental Stone
Tire Impression • What can we tell? – Tread style=tire model – Tread width=tire model – Distance of left tires from right tires (Track Width) – Manufacturer of tire and make and year of vehicle
Teeth Impressions • Can be left in food, gum and skin
Teeth Impressions • Connect suspect to bite mark:
Tracking and Animal Impression Analysis Think like an animal!
What controls the behavior of wild animals?
• Its Stomach • Its Hormones
Prey vs. Predator Tracks • Prey Animals – Many are Vegetarians – Tracks seldom go far from cover or burrows • Predator Animals – Need meat – Tracks visit every nook and cranny