Impression Evidence II 3D Impressions 3-D Impressions Impressed Evidence Typically found in exterior surfaces Shoe deforms surface Sand/soil/snow – other soft surfacesCharacteristics Vary widely Shallow or deep Quality varies Can have great detail or none 3-D Impressions Value of 3D Impressions Impressions with sufficient detail can be associated with a specific item of footwear Impressions in clay-based soil Can retain great detail Impressions in sand & small rocks Little detail Dry packed snow Greater detail than wet, melting snow Collecting 3D Impression Evidence Sequence Documentation Sketching Give lab knowledge where occurred @ scene Lab can recreate as closely as possible to original o Differences in how recreated in lab v scene can affect making proper match Field notes Photography Necessary for court presentation Casting Lifting Collecting 3D Impression Evidence Sequence Most impression evidence has 3D characteristics … surface topography. For forensic purposes, 3D impressions have depth in addition to length and width and commonly found outdoors in a soft or malleable receiving surface such as soil, sand or snow. The quality (detail) varies with, The receiving surface’s malleability, texture and composition. The detail present in the source origin. The mode by which the impression was transferred to the surface. The affects of weather: temperature, rain and snow. Collecting 3D Impression Evidence Sequence The scene investigator has no control over how the impression was generated or its clarity. Responsibility: capture detail as completely and as clearly as possible. Two activities: 1. Photography and 2. Casting. Casting defined: “the filling of a three-dimensional footwear impression with a material that will acquire and retain the characteristics that were left in that impression by the footwear.” Each archiving technique complements the other Photography and casting are not an either or decision. Both are critical and both must be done in order to properly archive the impressions. Lifting & Preserving 3D Footwear Impression Evidence What to Cast Indented (Impressed) Dry Impressions Wet, 2D Prints on Concrete Impressions in Snow Impressions Covered by Water Photography -v- Casting Photography Casting Shows impression as found at the scene Direct mold of the original impression Condition and detail Reproduces microscopic characteristics Can give best reproduction from coarse surfaces Gives reproduction of sides of outsoles not reproduced in photographs A backup for casting Backup for photography Casting Footwear Impressions Characteristics of Forensic Quality Casting Material Produce very fine detail Flow easily into impression Cleaned without loss of detail Easily obtained with consistent quality & properties Easily mixed – not require special equipment Set in reasonable time Unlimited shelf life Quality of Casts Receiving surface malleability, texture & composition Sand Clay Loamy soil Detail present in the impression Mode by which impression transferred to the surface Mechanics of making the impression Effects of weather: Temperature Rain/snow Wind Casting Gypsum manufacturing processes CaSO4-2H2O 110-130 Deg C Gypsum Calcium Sulfate Dihydrate Open Oven (CaSO4)2-H2O 130-200 Deg C Plaster Calcium Sulfate Beta-hemihydrate Autoclave Pressure Steam CaSO4 200-1000 Deg C Stone Calcium Sulfate Alpha-hemihydrate Plaster of Paris Dental Stone Requires more water Irregular Crystals & Porous Consistency > 50 Requires less water Uniform Crystals Dense Crystals Consistency < 50 Choosing Dental Stone Several kinds of dental stone … always check the compression strength measured in psi (pounds per square inch). Regular plaster of Paris is 5,000 psi compression strength and will chip fairly easily. Hydrocal is around 8,000 psi and is more durable. Merlin's Magic is around 14,000 psi and is even more durable yet. Excalibur and Die-Keen are 18,000 psi and dry so hard it's almost like a ceramic material. Casting Footwear Impressions Gypsum Consistency vs Compressive Strength (psi) Consistency Plaster per pounds of water Dry compressive Strength (psi) 50 2lbs-0oz 3750 38 2lbs-10oz 7000 33.3 3lbs-0oz 9750 30 3lbs-3oz 11,000 21 4lbs-12oz 15,000 Water-to-Powder (W:P) ratio Lbs per 100lb plaster W:P – The quantity of water (by wt.) per quantity of powder (by wt.) A “30 Consistency” means – 30 parts of water/100 parts powder Higher the consistency – longer setting times – lower strength - softer Mixing Merlin's Magic Merlin's Magic: Special type of casting material. Made to pour into molds easily with very few air bubbles. Mix differently than for regular plaster. Below are instructions to mix up enough plaster to fill one regular size mold. First you need to make a measuring cup that can be reused. http://www.hirstarts.com/casting/dental.html Procedure for Merlin’s Magic Need two disposable plastic cups - nested. Pour 2 ounces (60 ml) of water into the top cup and place a black mark on the outside of the bottom cup where the water line is. Place an additional 2.5 ounces of water into the cup (for a total of 4.5 ounces or 135 ml). Place another black mark on the outer cup at the water line. Remove the inner cup and you have a reusable measuring cup. Here is how you mix the plaster Insert a new cup into your measuring cup. Pour in water until it reaches the first line. Carefully shake in the powder until the mixture reaches the second line. The powder must be absorbed into the water before you can determine if the second line is reached. Remove the inner cup, mix up the plaster and pour it into your mold. Mixing by weight, Ounces (or ml) of water Amount of powder (by weight) 1 2 ounces (60ml) 186 grams 2 4 ounces (120ml) 372 grams 3 6 ounces (180ml) 558 grams 4 8 ounces (240ml) 744 grams Use table @ right. Need scale to Number of molds to fill measure the weight of the powder. "ounces" shown here are a liquid measurement (not weight). Mixing instructions on the package of Merlin's Magic will be different. Their instructions are used for dental castings, which use a vibrator to shake thicker plaster into their dental molds, which can give mix that is too thick to pour into a mold. Casting Using Dental Stone Photographing the Impression Proper positioning of scales Positioning of Retainer Placing the casting frame in place Mixing water (3/4 cup/lb stone) and dental stone Pouring mixture onto impression Curing the cast Allow to sit 30-40 minutes before lifting Do not remove adhering soil Final cast Allow to cure up 24-48 hours Carefully remove soil Save Soil for comparisons Casting Underwater Impressions Drain or remove excess water – Good – BUT - Not Necessary Pipette or syringe Carefully Absorb with paper towel Pour casting material as usual If water can’t be removed? Frame the impression Sift dry casting powder gently into water above impression Allow to fall to bottom Sift until 1” of powder covers the area Powder builds up & saturated with powder Use additional dental stone slurry to fill the framed area Will settle into the water later & into impression – cover entire impression Casting in Snow Casting Procedure Spray Impression with Snow Print Wax or Dust with Snow Print Powder 2-3 layers Allow to dry for 2-5 minutes between applications Slowly Add slightly cooled dental stone Cooled dental stone minimizes melting the snow Non-Casting Procedure Auto primer spray paint before Snow Print Better contrast for Photographs Photos critical Can’t directly cast with primer paint Many snow prints not cast Snow Casting Procedure Spray the impression lightly with the Snow Print Wax at an angle in order to highlight the raised areas of the impression. Do not cover the entire area of the impression. This is the best time to photograph the sprayed impression. Do not hold the spray too close to the impression because the blast from the aerosol can damage the impression’s detail. Spray the impression with 2 or 3 more applications, ensuring that the entire impression is covered in wax. A properly sprayed impression will not reveal much detail when viewed from above. The red (or other colored sprays) attracts heat: Shield the impression from the sun. Allow the wax mold to dry for approximately 5-10 minutes. Prepare a dental stone slurry and allow it to sit longer than usual so that when the slurry begins to harden, the heat generated will not melt the impression. When the cast is hardening, scratch initials and date into the cast. Allow the impression to sit for approximately 60 minutes before lifting. After lifting, immediately photograph the cast. Snow print casts are fragile, and the wax molding is easily destroyed. Keep the cast away from sunlight. If melting occurs, cast detail may 3D Scanning Snow Print Wax Casting with plaster 3D surface scanning GOM ATOS II system (Gesellschaft fu¨r Optische Messtechnik mbH, Braunschweig, Germany). 3D model of the sole http://cs.iupui.edu/~tuceryan/pdf-repository/Buck2007.pdf Packaging Casts Allow cast to dry for 24 hours or longer Do not attempt to remove soil or clean until cured Will destroy impression Soil used for comparison purposes Loosely & individually wrapped in paper or paper bag Do not wrap in tight plastic Place wrapped cast in cardboard box & tape seal Place in shock absorbent or porous packaging material Illinois State Police Packaging Procedure for Cast Impressions Identification: Before cast hardens, place CSI or investigator’s initials, date and case & number on back side of cast. Amount Desired: Standard -Evidence - Up to 2 ft. Preservation: Use mesh reinforcing and let dry 24 hours before putting in package. Wrapping & Packing: Surround with packing material in box too prevent shifting or breakage. Avoid sealing in plastic bags. Miscellaneous: Dental stone is the preferred casting material. Take photos of impressions before casting. Mark package FRAGILE. Do not clean. Do not use twigs for reinforcement. http://www.isp.state.il.us/docs/6-420.pdf Impression Evidence On-Scene Overview  Impression And Surface Category of Impression Wet soil or Mud (fine, even consistency) 3D Photograph 1. Dust with black/fluorescent or bicolor magnetic powder Cast using dental stone Concrete 2D Photograph quickly 1. Quickly dust with black/fluorescent or bicolor magnetic powder 1. Re-photograph 2. Cast using dental stone In dry soil (Hard, packed or loose. Varying in consistency from coarse to powderfine) 3D Photograph 1. Stabilize with hair spray or lacquer 2. Spray with automotive primer paint of appropriate contrasting color 1. Re-photograph 2. Cast using dental stone Sand (variable texture – retains small amount of impression detail) 3D Photograph 1. Stabilize with spray paint (black) or “snow print wax” or “snow print powder” 2. Spray with automotive primer paint. 1. Re-photograph 2. Cast using dental stone Archiving Method Enhancement Method Adapted from Hilderbrand, Dwane S. Footwear, The Missed Evidence, Skaggs Publishing 1999, pages 61-62. Preservation Method Impression And Surface Category of Impression Archiving Method Enhancement Method Preservation Method Snow (Temperature affects textures, cohesiveness and impression detail) 3D Photograph 1. Stabilize with automotive primer paint (gray) and/or “snow print wax or powder” 2. Spray with automotive primer paint. 1. Re-photograph 2. Cast using dental stone or Jade Stone Dry Residue - Dust on Hard Surfaces (Produce highly detailed impressions on hard surfaces) 2D Photograph 1. Lift using electrostatic or gelatin lifter) 2. Chemical enhancement. Re-photograph Wet Residue – Dust or Mud on Hard Surfaces (Highly detailed impressions) 2D Photograph 1. Cannot be lifted using electrostatic lifter. Can be lifted using gelatin lifter 2. Dust with magnetic powder (dual color or black) 3. Treat for the presence of iron or other metals 4. Cyanoacrylate fume followed by powder dusting or fluorescent staining (surface dependant) 1. Re-photograph 2. Lift with gel lifter Dust – Fabrics (Carpet, upholstery & bedding can produce detailed impressions within the fabric nap or on the surface) 2D Photograph 1. If dust – lift as above. 1. Re-photograph 2. Cast using Jade Stone … or 3. Lift with gel lifter Blood (Can produce high-detail impressions) 2D Photograph 1. Light surfaces – Stain using Acid Violet 17. 2. Dark surfaces – stains using Basic Yellow 7 or DFO. 1. Re-photograph 2. Lift using gelatin lifter. Exemplar Impressions Exemplar Footwear Impressions Many people leave impressions @ scene Categorize designs of shoes Victims Witnesses Medical personnel Other innocent people Officers Suspects Known impressions made Specialty impression materials available Biofoam http://site.utah.gov/dps/impressions-fw-evidencecollection_000.htm Gellifter Inkless Lifter http://site.utah.gov/dps/impressions-fw-evidencecollection_000.htm Forensic Footwear Databases TreadMark™ The number of shoe prints at a crime scene can be so large that the process of impression recovery becomes very time-consuming. Commercial product using four parameters—pattern, size, damage, and wear—to identify individual outsole impressions. Compared with shoe print data from two sources: suspects in custody and crime scenes. A match could yield the name, date of birth, criminal record number, places of interest, and similar offenses for possible suspects. How does TreadMark™ work? Impressions from crime scene obtained using photograph, gel lift, dust lift, and adhesive lift. Input directly into the analytical system by high-resolution digital imaging. Same procedure used with impression of a suspect’s shoe print: Operator measures, analyzes, and compares crime-scene and suspect images. Both image sources can be searched within themselves and against each other, allowing such images to be transmitted to other users. www.csiequipment.com/systems.aspx Exit Notice. SoleMate Commercial database contains information—manufacturer, date of market release, an image or offset print of the sole, and pictorial images of the uppers—for more than 12,000 sports, work, and casual shoes. Sold on DVD, updated and distributed to subscribers every 3 months. Limitation is that different manufacturers often use the same sole unit. Therefore, it may be difficult to determine the exact make and model of a shoe. The software links such records, however, so that all footwear that might match a crime-scene print can be considered. How does SoleMate work? The pattern of an unidentified shoe print is assigned a set of codes to isolate basic features, such as circles, diamonds, zigzags, curves, and blocks. Options, with variations, are presented pictorially, allows investigator to code features that best match the shoe print. These codes form the database search, with results presented in descending order of pattern correlation. Foster & Freeman USA Inc., at 888-445-5048. TreadMate Maintained by the same United Kingdom company that markets SoleMate, this database contains information: 5,000 vehicle tires and tire tread patterns, Manufacturer, Date of market release, Pictorial image, Pattern features. Because manufacturers sometimes use the same tread, it may be difficult to find the exact make and model match of a tire. In these cases, records are linked so that all tires that might match a crime-scene tire mark may be considered. How does TreadMate work? The pattern of an unidentified tire mark is assigned a set of codes for pattern features, such as waves, lines, diamonds, zigzags, curves, and blocks, which then form the basis of the database search. Results are presented in descending order of correlation. Foster & Freeman USA Inc., at 888-445-5048 or [email protected] Tire Print Evidence Evidence Often Overlooked Vehicle-Involved Scenes Vehicle-involved scenes run the gamut of scene types: homicides, sexual assaults, burglaries, drive-by shootings, terrorist events, etc. Identifying vehicle should be a critical aspect of any onscene investigation. In typical homicide investigation, investigators must consider the possibility that specific categories of physical evidence related to the crime are present. Hit and run crimes, whether vehicle-vehicle, vehicleperson, vehicle-other object, involve vehicles that leave the scene. In these crimes, damage creates physical evidence Evidence could prove the culprit vehicle was at the scene; o This evidence should be collectable. The following article from the New York Daily News is such an example. In this case, the suspect and his vehicle were found. The NYPD crime scene unit had the responsibility of working the car to prove it was the vehicle that struck the victim. Case Example Kidnapping Hypothetical - Kidnapping Involves a vehicle for transport Critical to find physical evidence that the child had been inside the car, Reality: Such evidence may not be present or had been removed. The abducted child case. No evidence found inside the suspect vehicle proving the child there … Must consider other, indirect, avenues to move investigation forward. The abductor vehicle had been at the scene. Success includes thorough investigation of the outside where the vehicle might have been parked Physical evidence collected and scene archived. One example of physical evidence vehicles leave behind is tire track impressions. Tire Track Impression Evidence Evidence Often Overlooked Footwear Impression: Dealt with locating, enhancing, photographing, etc, footwear impression evidence, Much of that discussion is applicable to tire track evidence as well. Similarities with Footwear Impressions Tire track evidence: Classified as two-dimension (2D) or three-dimension (3D). Commonly in dust or are otherwise contaminated 2D impressions or impressions in a soft surface. Considered Class or individualizing: Physical characteristics needed for meaningful criminalistic-quality comparisons Former provides information about the tread design Latter provides information imbedded into the tread of the tire from daily usage. Footwear & Tire Track Differences Their Intrinsic Forensic Values Provides evidence of the individual (shoe impressions) or the vehicle (tire impressions) being at the scene, For tire tracks, suggests the individual vehicle was used in the crime. Tire track impressions geared to identify vehicle … not the person, Although the person might have been driving the vehicle. How Important is Scene Evidence? Identifying specific vehicle requires recovering it and making direct comparisons with physical evidence from scene Scene data allows investigators and laboratory analysts to narrow the search among universe of vehicles. Until suspect vehicle is located and impounded, all scene data must be archived, collected and preserved. Determining which tire tracks to photograph, enhance and or cast is critical Critical Vehicle Information Crime Scene Procedures How vehicle was maneuvered? Vehicle characteristics Stance Track measurements Wheelbase Tread wear indicators Wear bars No. vehicles & no. occupants Were objects loaded or unloaded? Direction of travel Relationship of impressions @ scene to arrangement of tires on suspect vehicle Position of front of vehicle Which impressions made by front & rear tires Which impressions to photo/cast Locations where vehicle track measurements will be recorded Other relevant evidence Footwear impressions Fluid spills On-Scene Considerations Success At the Scene One Shot at It Unknown: Whether something seemingly unimportant and ignored will be important as evidence AND suddenly plays a prominent role in the investigation. Consider everything at vehicle-involved scenes as potentially probative. Misperception that tire track impressions have little forensic or investigative value. General scene investigative principles apply equally to vehicleinvolved scenes; Management, archiving, searching, etc, are an integral aspect of the investigation. Crime Scene Procedures Secure the area Discrete Security Areas at the Scene Tire prints protected Obtain information Case information Vehicle information Scene information Public Establish safe path to view evidence Archive Collect/package/preserve evidence Segregated Witnesses & Potential Suspects Official Busines s Official Busines s Media Scene & Command Center Secure Travel Routes for Emergency Equipment / Personnel Public Management Should employ guidelines previously discussed While these principles are inviolate Unique characteristics for vehicle-involved scenes. Specifically, identifying, archiving, characterizing and preserving the physical evidence associated with identifying a suspect vehicle. Investigative Questions Archiving Sketching and critical on-scene measurements Vehicle information Suspect information Reconstruction Archiving Archiving Photographing, sketching, video, 3D-Imaging tiretrack and other vehicle-involved scene evidence Much like for footwear impression evidence. For tire track impressions – Document at least 24” of impression For comparison purposes Photography of Tire Track Impressions. Photos must Include markers that Identify the tire position on vehicle – Establishing or Overview Photographs • Tell the story and relationship of how the tire tracks relate to the overall scene. Photos with and without evidence markers in place. – Midrange • Tell the story of how the tire track evidence relate to each other and to nearby objects. Photos with evidence markers are important to establish evidence-to-evidence relationships. – Close-ups • These include at least 24” of all 4 impressions, appropriately identify which tire, e.g., right front, etc, being photographed. Photos with and without scales must be included. Considering Lighting and Glare 3-D Impression Blocking Sunlight Using Ambient Light Photographing 3-D Impressions Photograph before casting Reproduces class characteristics Accidental characteristics are often lost Spray paint may enhance sufficiently Outdoor lighting may make it necessary to block direct sunlight Sometimes sunlight may be superior to oblique lighting Use polarizing filters to eliminate glare Look for sidewall information in impression Photography – Effect of Lighting •Existing light blocked out and oblique light provided with off camera Flash Archiving 3D Impressions Casting http://projects.nfstc.org/ipes/presentations/Bodziak_Footwear-Non.pdf Archiving 3D Impressions Casting Tire Impressions in the Snow Reverse Sidewall Impression Marking Tire Impression Evidence Vehicles Still at the Scene Photographer’s name, Date, Time Use scales in plane of impression Mark tire position on vehicle & on scene Use spray fluorescent paint for all wheels Rt front, etc Arrow pointing to front of vehicle Establishes inside & outside edge of impression Impression number 1st or 6th impression recorded @ the scene N/S directional Sketches Tire Track Impressions Plan sketches: Overview of impressions In-Depth detail not important Measurements Photography Archiving – Sketches Include Vehicle-Critical Measurements Sufficiently detailed to permit a determination of specific vehicle characteristics Dependent on the amount and detail of the tire track impressions present. Appropriate measurements must be made. The measurements are the critical data needed to compare the on-scene tracks with a suspect vehicle. Anatomy of the Tire Tread Design http://www.jacks-tire.com/Tire101.aspx Pitch Eliminating Road Noise Pitch Large Small Medium Medium Small Vehicle Information How Was the Vehicle Maneuvered? Direction of Travel Closely examine tire tracks Using known factors Common sense Direction of Travel Spinning tires Striations by sidewall in furrow Shows which way tire rolling Location where vehicle stopped, backed up to change direction Overlapping front & rear tire tracks Look to see if coming or going from scene Grass or small plants Direction they were flattened Directional tire tread patterns Damp soil or snow Tires lifted soil or snow slightly in direction of travel Deposition of transferred material in direction of travel Mud, dirty water or fluids splashed or thrown in direction of travel Make the Appropriate Tire Track Measurements Wheelbase Front track width Rear track width Turning diameter Tread design width (arc width) Tread depth (skid depth) Tire circumference Wheelbase Defined as the distance between the leading edge of the front and rear tires. Front Tire Track Width Approximate Wheelbase Rear Track Tire Width Front Tires Turned Wheelbase Front Wheels Turned Inside leading edge of track will be rounded Make rt. Angles to center line of impression Will run laterally across the width of impression Project line along inside edge – parallel to center line o Intersection is fixed point on inside leading edge o Repeat of all 4 tires Wheelbase in Mud & Snow Camber http://autorepair.about.com/od/glossary/ss/def_camber.htm http://en.wikipedia.org/wiki/Camber_angle Camber Tilt” of the tires as they rest on the ground. Mechanical issues with vehicle affect how impressions appear at scene Differences between normal and abnormal camber (positive or negative) signifies improper alignment or worn front-end parts of the vehicle. Positive camber: tires tilted further apart, “out,” at the top. Negative camber tires tilted closer, “in,” at the Normal Camber Narrower Positive Camber Tire tilted “out” @ top top, Wider Negative Camber Tire tilted “in” @ top Track Width or Stance Front and Rear Track Widths Defined as distance between middle of leading edge of the front and back tires. Front and Rear Track Widths • Track widths – Midpoint of leading edge of Mechanical issues can affect front and rear tire track how these impressions appear at impressions the scene. Among others, one is camber, which is the “tilt” of the tires as they rest on the ground. Front Tire Track Width Rear Track Tire Width Track Width Toe In or Out Toe Difference between front & rear of front tires Normally set “in” only a few millimeters o Compensate for normal front end tendency to toe “out” at highway speeds. Improper alignment Worn front end components Vehicle Information Turning Diameter Turning diameter Diameter is defined as the diameter of the circle made when the vehicle is driven in a circle. Determined from measurements taken @ scene. At the scene Don’t know if the turn is full-lock Curb-to-curb for the outer tires Not wall-to-wall for outside edge of vehicle Turning Diameter Procedure Select segment reflecting sharpest portion of turn Measure imaginary line between 2 points of arc Measure outer margin to outer margin A-AA Calculating Turning Diameter A C B E Bisect line & draw line to outer margin of track arc – (C-B) Calculate diameter AA Rear Tire (A-C) Draw another line between the bisect point and the inside of the track arc – F Front Tire On-Scene Tire Impression BD Bisects A – AA @ C: Line E= Distance B to C Distance C to AA = Line F (= distance A to C) 2 Turning Diameter = (F / E) + E (11) Alternatively: Turning Diameter = (F 2/8E + E/2) (12) Tire circumference Approximate the tire circumference by finding an accidental, repeated characteristic, such as a gouge or cut, along the imprint. The distance between these repeated marks is the rolling tire circumference. Investigators must understand that measured value – accidental characteristic-toaccidental characteristic – different from value obtained by wrapping the measuring tape around the tire in its center line, Larger Procedure Measure distance between repeated accidental characteristics on impression Considerations Measured value is less than when the tape is wrapped around the tire o Tires have a curved arc width, impressions do not. Measured circumference is larger in the center line of the tire than at the outer edges. Vehicle Information Tread Design Tread design width (arc width) Tread design width: Measurement from one edge of the design to the other. These measurements must be measured at the scene from the impression. Information important so manufacturers can help investigators identify an unknown impression. Non-dirt Impressions 2D impressions visible because of contaminants adhering to the tread; dirt and dust the most common. Other contaminants also create impressions water, grease (oil) or blood. Each leaves visible impression Each can be enhanced, depending on the contaminant. Consideration of Enhancement Choices Variety of choices and investigators must make the proper decision. Archiving the impression photographically is step-one Enhancement choices and the variables offered by the scene: o Surface material, o Chemistry of the impression material (dirt, oil, blood, etc), and the o Chemistry of the enhancement method. Tread Wear Tread Wear Indicators Tread wear indicators (wear bars) Located in grooves of tread design Run laterally across tread o 1/16” above base of the groove Useful for comparison purposes o Divide tire into useful segments Cars & light trucks 6 evenly spaced o Rim diameter of 305mm/12 inches must have @ least 6 o Less than 305mm must have @ least 3/12 inches Wear Bar Indicator Tread Wear First thousand miles produces the fastest tread wear As elements become shorter Flex less & squirming is reduced Slows considerably Accidental characteristics last longer on well-worn tire than on a new one Tire wear indicator Factors Affecting Tread Wear Excessive under-inflation Excessive over-inflation Balancing Improper toe-in-out Improper camber Chunking Faulty breaks Combined suspension steering issues Bad repairs Measuring Tread Depth Non-Skid Depth Equipment: Tread depth gauge (Measures in 1/32nds) or 15mm ruler Newer tires: 11/32 to 16/32” Maximum depths suggest newer tires Wear bars are set @ 2/32nds, Wear patterns appear as solid bar in the tire impression Procedure Estimate height of groove in scene impression Set depth gauge on impression groove Carefully lower gauge into impression & read depth from the scale Alternatively, measure depth from cast in dental stone Tread Depth - Some Statistics When tires near end of life, U.S. Lincoln penny can be used to confirm the tire's tread depth. If Lincoln's entire head is visible, the tire is worn to approximately 2/32" and is considered legally worn out in most States. Average new tires used on cars typically start with 10/32" to 11/32" of original tread depth. Dedicated winter / snow tires and light truck tires typically are deeper - how much deeper depends on tire's tread type ... Highway Rib, Highway All Season, Off Road All Terrain or Off Road Maximum Traction). Means - original tread depth has only 8/32" of useable tread depth. Useable tread depth calculated by subtracting a worn out tire's 2/32" from the new tire's original depth of 10/32". The final 2/32" of a tire's tread depth isn't part of the equation when it comes to calculating tread depth percentages because the tire is already legally worn out. Remaining tread depth used to calculate tread wear percentages. … oTire that started with 10/32" of original tread depth and has worn off 4/32" (down to 6/32" of remaining tread depth) is 50% worn. o 2/32" legally worn out tread depth A tire that starts with 10/32" of original tread depth has 12.5% wear for every 1/32" that is worn away, and a tire that starts with 12/32" " of original tread depth, has 10% wear for every 1/32" that is worn away, http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=197 Identifying Tread Wear Exposed tire bars 2/32 Tread Legally Worn Tire bars recessed in sipes & grooves become exposed 4/32 Tread • Circular wear Wear around circumference w/sipes & grooves indicates wear 6/32 Tread Enhancing Tire Tracks Enhancing Tire Track Impressions Involves many of the same principles as for footwear evidence Photography : A method for archiving AND enhancing. Chemical enhancements. Chemical treatments take advantage of the inherent chemical signature of the impression o Minerals, such as iron and aluminum, etc, organics, or bio-materials – to more clearly visualize the impression. The chemical enhancements are essentially the same those used to enhance footwear evidence. Chemical Enhancement Metals in Soil Impressions with Metals Ammonium or Potassium Thiocyanate Tests for Iron Reddish brown 8-Hydroxyquinoline Iron, magnesium + other metals Fluorescent under UV light Impression w/oil or fats Iodine fuming or Iodine crystals Oils & Other organic compounds Iodine absorbed Enhancement Benzophenone o Forms stable blue color Thin layer of starch powder o Subsequent steam treatment turns starch blue Chemical Enhancement Wet Tires with Salt Deposits - Winter • Silver Nitrate – Converts NaCl (salt) to AgCl (Silver Chloride) • NaCl + AgNO3 Road Salt 2% Silver Nitrate In Methanol AgCl + AgNO3 hv Ag Metal – UV or sunlight darkens impression Tire Tracks in Blood Chemical Enhancement Blood reactive chemicals DAB Leucocrystal Violet Acid Violet 17 Acid Yellow 7 – dark surfaces – yellow fluorescence Amido Black Ninhydrin DFO Crowle’s Stain TMB Coomassie blue Nile Red Hungarian Red Ashley’s reagent Investigative Evidence Identifying Unknown Vehicle Tire Impressions as Investigational Aids Identifying manufacturer & brand name Done after processing the scene Tread design Who makes it & where Tire guides – Boca Raton, FL Shows tread patterns for all types of tires sold in the U.S. Comprehensive Visual Identification of all types of Tire Tread Pattern Designs. Covers Passenger, Light Truck and Medium Truck vehicles. Includes Off-Road and Agricultural Tread Patterns. Also covers Motorcycle and retread tire tread designs. Provides information on how to read a tire sidewall and on the different Tire Sizing Systems. Gives detailed information on Speed-Rating and Load Indexes as well as lug nut torque and tightening sequences. http://tireguides.com/Products/245 On-Scene Information Limited Slip Differential (LSD) Posi-traction One wheel was spinning o Movie: My Cousin Vinnie o Can narrow type of vehicle Odd mixture of worn tires Suggests an older vehicle Possible alignment problems Stolen items - gasoline Location of gas tank o Check footprints @ side of car where gas tank located Estimate from amount taken whether a truck (pickup-SUV) Mechanical Problems Mechanical Problems & Vehicle Design Features Fluid leaks @ scene Oil, antifreeze, brake fluid, trans fluid Collect for chemical analysis @ lab Vehicle Location History Foreign Material on Suspect Vehicle Notice unusual material in tread impression Collect & take to lab Identifying The Correct Impression Age of Tire Impression How Long @ Scene • How long an object (driven over) has been lying on the ground – Complainant may have this information • Transferred substance – Recently spilled Fluid • Knocked over objects • Weather conditions prior to offense – Help date time of deposit of scene impression Known Tire Impressions Known Tire Impressions Need one full circumference of the tire Complex pitch in modern radials Might miss important accidental characteristics Taking Tire Impressions Methods & Materials needed Large area to make impression Broom Vehicle lift Tire marking crayons Rag to clean dirt from tires Roll of paper towel Large jar of Petroleum Jelly (Vaseline) Gloves Art board 15” x 40” (3 pieces/tire) Lg & sm felt marking pens Magnetic jet black print powder 3” wide magna brush Strips of polyester plastic 12” x 40” to protect impression Scotch tape to attach plastic to art board Information From Each Tire • ID each tire later • Photograph Tire – – – – Exterior sidewall Tread design Serial number Design, mold & drawing numbers • Show up after rubbing w/crayon – – – – Manufacturer Tire brand name Tire size Type of tire • Summer, etc – Construction • Radial, bias ply, etc – Other numbers • Mold, design, etc – Wear – Number of ribs in design Recording Known Tire Impressions Recording known tire impression Art board is superior to paper Small debris on surface can’t come through Reduces/eliminates wrinkles/tearing common with paper Use gloves to keep board clean 3 pieces of 40” Board sufficient to record 1 full circumference of tire Tread Wear Indicators Recording Known Tire Impressions Petroleum Jelly/Magna Brush Method – 2D Place 2 pieces of art board in path of vehicle travel Tape on reverse side to hold pieces together Mark adjoining pieces appropriately Push car over recording surface Vaseline leaves light brown impression Mark on art board as each tread wear indicator (marked on sidewall) rolls by Mark spaces on art board to correspond to numbers on known tire Tire Wear Indicator Marks Place locations on sidewall Recording Known Tire Impressions Petroleum Jelly/Magna Brush Method – 2D Cover art board in front & behind impression w/paper towel to protect it Clean area of tire that was on the floor when Petroleum Jelly first applied Apply Petroleum Jelly to this area and push car again Recording Known Tire Impressions Vaseline/Magna Brush Method – 2D Near end of second art board Stop vehicle Remove 1st piece of art board Add thin coat of Vaseline to tire Place 3rd piece of art board in path of vehicle Continue pushing until known impression is transferred to this 3rd section Recording Known Tire Impressions Petroleum/Magna Brush Method – 2D • Dust impression as soon as possible – Waiting too long causes defined areas of tread to diffuse into art board surface • Brush with magnetic brush @ rt. Angles w/swirling action – Avoid dusting clear areas of board – Black magnetic Dusting Powder Recording Known Tire Impressions Vaseline/Magna Brush Method – 2D Protecting the impression Cover with clear acetate to prevent smearing or damage during transit & comparison process Allows examiner to draw lines during comparison Recoding Known Tire Impressions Inking Method I Apply ink to art board for 1 full circumference Fingerprint Ink works Push car (tire) over inked art board This is the inking process Push car over clean strip of white art board to record the impression Recording Known Tire Impressions Inking Method II: Transparent Method Ink the tire as in inking method Drive tire over transparent acetate or other transparent media (Mylar) Tape to art board - suitable solid backing Advantages Can be rolled up for storing Unrolled @ later time for comparison Can be compared directly to impression when searching for Comparing Scene Cast with Acetate Exemplary Overlay Comparing Scene Cast Actual Exemplar Tire The area defined by blue tape is the segment of the right rear tire which corresponds with the crime scene cast.