3 3-D Impressions Impressed Evidence Typically found in exterior surfacesShoe deforms surfaceSand/soil/snow – other soft surfacesCharacteristicsVary widelyShallow or deepQuality variesCan have great detail or none
4 3-D Impressions Value of 3D Impressions Impressions with sufficient detail can be associated with a specific item of footwearImpressions in clay-based soilCan retain great detailImpressions in sand & small rocksLittle detailDry packed snowGreater detail than wet, melting snow
5 Collecting 3D Impression Evidence Sequence DocumentationSketchingGive lab knowledge where sceneLab can recreate as closely as possible to originalDifferences in how recreated in lab v scene can affect making proper matchField notesPhotographyNecessary for court presentationCastingLifting
6 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.
7 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 otherPhotography and casting are not an either or decision. Both are critical and both must be done in order to properly archive the impressions.
8 Lifting & Preserving 3D Footwear Impression Evidence
9 What to Cast Indented (Impressed) Dry Impressions Wet, 2D Prints on ConcreteImpressions in SnowImpressions Covered by Water
10 Photography -v- Casting Shows impression as found at the sceneDirect mold of the original impressionCondition and detailReproduces microscopic characteristicsCan give best reproduction from coarse surfacesGives reproduction of sides of outsoles not reproduced in photographsA backup for castingBackup for photography
11 Casting Footwear Impressions Characteristics of Forensic Quality Casting Material Produce very fine detailFlow easily into impressionCleaned without loss of detailEasily obtained with consistent quality & propertiesEasily mixed – not require special equipmentSet in reasonable timeUnlimited shelf life
12 Quality of Casts Receiving surface malleability, texture & compositionSandClayLoamy soilDetail present in the impressionMode by which impression transferred to the surfaceMechanics of making the impressionEffects of weather:TemperatureRain/snowWind
13 Casting Gypsum manufacturing processes CaSO4-2H2ODeg CGypsumCalcium Sulfate Dihydrate(CaSO4)2-H2ODeg CPlasterCalcium SulfateBeta-hemihydrateCaSO4Deg CStoneCalcium SulfateAlpha-hemihydrateOpen OvenAutoclavePressureSteamPlaster of ParisRequires more waterIrregular Crystals & PorousConsistency > 50Dental StoneRequires less waterUniform CrystalsDense CrystalsConsistency < 50
14 Choosing Dental StoneSeveral 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.
15 Plaster per pounds of water Casting Footwear Impressions Gypsum Consistency vs Compressive Strength (psi)ConsistencyWater-to-Powder (W:P) ratioLbs per 100lb plasterPlaster per pounds of waterDry compressive Strength(psi)502lbs-0oz3750382lbs-10oz700033.33lbs-0oz9750303lbs-3oz11,000214lbs-12oz15,000W:P – The quantity of water (by wt.) per quantity of powder (by wt.)A “30 Consistency” means – 30 parts of water/100 parts powderHigher the consistency – longer setting times – lower strength - softer
16 First you need to make a measuring cup that can be reused. Mixing Merlin's MagicMerlin'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.
17 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
18 Mixing by weight, 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,Use right. Need scale to 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.Number of molds to fillOunces (or ml) of waterAmount of powder (by weight)12 ounces (60ml)186 grams24 ounces (120ml)372 grams36 ounces (180ml)558 grams48 ounces (240ml)744 grams
19 Casting Pouring Procedure Release agent Lightly mist above impression with hair sprayA controversial procedureKeeps integrity of the detail intactCan also use commercial hardening productsDirt HardenerTalc powder seems to work as well as anythingUse “baffle” about 2” above imprint & tipped at shallow anglePaper covered clipboardOr strong cardboardPour casting material onto baffle & allow uniform flow onto imprintAvoid irregularities or “waves” in plasterAllow first pour to become firmPrepare second batch – if necessaryAfter hardening scratch identifying information into surface with dowel or knifeCastingCastingMaterialCastingMaterialBaffle/HandImpressionIn Mud
21 Photographing the Impression Proper positioningof scalesPositioningof Retainer
22 Placing the casting frame in place Mixing water (3/4 cup/lb stone)and dental stonePouring mixture onto impression
23 Curing the cast Final cast Allow to sit minutes before liftingDo not remove adhering soilFinal castAllow to cure up hoursCarefully remove soilSave Soil for comparisons
24 Casting Underwater Impressions Drain or remove excess water – Good – BUT - Not NecessaryPipette or syringeCarefully Absorb with paper towelPour casting material as usualIf water can’t be removed?Frame the impressionSift dry casting powder gently into water above impressionAllow to fall to bottomSift until 1” of powder covers the areaPowder builds up & saturated with powderUse additional dental stone slurry to fill the framed areaWill settle into the water later & into impression – cover entire impressionAllow to set for at least 1 hour
25 Casting in Snow Casting Procedure Non-Casting Procedure Spray Impression with Snow Print Wax or Dust with Snow Print Powder2-3 layersAllow to dry for 2-5 minutes between applicationsSlowly Add slightly cooled dental stoneCooled dental stone minimizes melting the snowNon-Casting ProcedureAuto primer spray paint before Snow PrintBetter contrast for PhotographsPhotos criticalCan’t directly cast with primer paintMany snow prints not cast
27 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
28 3D Scanning Snow Print Wax Casting with plaster 3D surface scanning GOM ATOS II system (Gesellschaft fu¨r OptischeMesstechnik mbH, Braunschweig, Germany).3D model of the sole
29 Packaging Casts Allow cast to dry for 24 hours or longer Do not attempt to remove soil or clean until curedWill destroy impressionSoil used for comparison purposesLoosely & individually wrapped in paper or paper bagDo not wrap in tight plasticPlace wrapped cast in cardboard box & tape sealPlace in shock absorbent or porous packaging material
30 Packaging Procedure for Cast Impressions Illinois State PolicePackaging Procedure for Cast ImpressionsIdentification: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 orbreakage. Avoid sealing in plastic bags.Miscellaneous:Dental stone is the preferred casting material. Take photos of impressionsbefore casting. Mark package FRAGILE. Do not clean. Do not use twigs for reinforcement.
32 Category of Impression And SurfaceCategory of ImpressionArchiving MethodEnhancement MethodPreservation MethodWet soil or Mud(fine, even consistency)3DPhotograph1. Dust with black/fluorescent or bicolor magnetic powderCast using dental stoneConcrete2DPhotograph quickly1. Quickly dust with black/fluorescent or bicolor magnetic powder1. Re-photograph2. Cast using dental stoneIn dry soil(Hard, packed or loose. Varying in consistency from coarse to powder-fine)1. Stabilize with hair spray or lacquer2. Spray with automotive primer paint of appropriate contrasting colorSand(variable texture – retains small amount of impression detail)1. Stabilize with spray paint (black) or “snow print wax” or “snow print powder”2. Spray with automotive primer paint. Adapted from Hilderbrand, Dwane S. Footwear, The Missed Evidence, Skaggs Publishing 1999, pages
33 Category of Impression And SurfaceCategory of ImpressionArchiving MethodEnhancement MethodPreservation MethodSnow(Temperature affects textures, cohesiveness and impression detail)3DPhotograph1. Stabilize with automotive primer paint (gray) and/or “snow print wax or powder”2. Spray with automotive primer paint.1. Re-photograph2. Cast using dental stone or Jade StoneDry Residue - Dust on Hard Surfaces(Produce highly detailed impressions on hard surfaces)2D1. Lift using electrostatic or gelatin lifter)2. Chemical enhancement.Re-photographWet Residue – Dust or Mud on Hard Surfaces(Highly detailed impressions)1. Cannot be lifted using electrostatic lifter. Can be lifted using gelatin lifter2. Dust with magnetic powder (dual color or black)3. Treat for the presence of iron or other metals4. Cyanoacrylate fume followed by powder dusting or fluorescent staining (surface dependant)2. Lift with gel lifterDust – Fabrics(Carpet, upholstery & bedding can produce detailed impressions within the fabric nap or on the surface)1. If dust – lift as above.2. Cast using Jade Stone … or3. Lift with gel lifterBlood(Can produce high-detail impressions)1. Light surfaces – Stain using Acid Violet 17.2. Dark surfaces – stains using Basic Yellow 7 or DFO.2. Lift using gelatin lifter.
37 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.Notice.
38 Foster & Freeman USA Inc., at 888-445-5048. SoleMateCommercial 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
39 How does TreadMate work? 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 or
40 Evidence Often Overlooked Tire Print EvidenceEvidence Often Overlooked
41 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 on-scene 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, vehicle-person, vehicle-other object, involve vehicles that leave the scene.In these crimes, damage creates physical evidenceEvidence could prove the culprit vehicle was at the scene;This evidence should be collectable.
42 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.
43 Case Example Kidnapping Hypothetical - Kidnapping Involves a vehicle for transportCritical 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 parkedPhysical evidence collected and scene archived.One example of physical evidence vehicles leave behind is tire track impressions.
44 Tire Track Impression Evidence Similarities with Footwear Impressions Evidence Often OverlookedFootwear 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 ImpressionsTire 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 comparisonsFormer provides information about the tread designLatter provides information imbedded into the tread of the tire from daily usage.
45 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.
46 How Important is Scene Evidence? Identifying specific vehicle requires recovering it and making direct comparisons with physical evidence from sceneScene 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
47 Critical Vehicle Information Crime Scene Procedures How vehicle was maneuvered?Vehicle characteristicsStanceTrack measurementsWheelbaseTread wear indicatorsWear barsNo. vehicles & no. occupantsWere objects loaded or unloaded?Direction of travelRelationship of scene to arrangement of tires on suspect vehiclePosition of front of vehicleWhich impressions made by front & rear tiresWhich impressions to photo/castLocations where vehicle track measurements will be recordedOther relevant evidenceFootwear impressionsFluid spills
49 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 vehicle-involved scenes;Management, archiving, searching, etc, are an integral aspect of the investigation.
50 Crime Scene Procedures Secure the areaTire prints protectedObtain informationCase informationVehicle informationScene informationEstablish safe path to view evidenceArchiveCollect/package/preserve evidence
51 Management Investigative Questions Archiving Should employ guidelines previously discussedWhile these principles are inviolateUnique characteristics for vehicle-involved scenes.Specifically, identifying, archiving, characterizing and preserving the physical evidence associated with identifying a suspect vehicle.Investigative QuestionsArchivingSketching and critical on-scene measurementsVehicle informationSuspect informationReconstruction
53 ArchivingPhotographing, sketching, video, 3D-Imaging tire-track and other vehicle-involved scene evidenceMuch like for footwear impression evidence.For tire track impressions – Document at least 24” of impressionFor comparison purposes
55 Considering Lighting and Glare 3-D Impression Blocking Sunlight Using Ambient Light
56 Photographing 3-D Impressions Photograph before castingReproduces class characteristicsAccidental characteristics are often lostSpray paint may enhance sufficientlyOutdoor lighting may make it necessary to block direct sunlightSometimes sunlight may be superior to oblique lightingUse polarizing filters to eliminate glareLook for sidewall information in impression
57 Photography – Effect of Lighting Existing light blocked out and oblique light provided with off camera Flash
60 Tire Impressions in the Snow Reverse Sidewall Impression
61 Marking Tire Impression Evidence Vehicles Still at the Scene Photographer’s name, Date, TimeUse scales in plane of impressionMark tire position on vehicle & on sceneUse spray fluorescent paint for all wheelsRt front, etcArrow pointing to front of vehicleEstablishes inside & outside edge of impressionImpression number1st or 6th impression the sceneN/S directional
62 Sketches Tire Track Impressions Plan sketches: Overview of impressionsIn-Depth detail not importantMeasurementsPhotography
63 Include Vehicle-Critical Measurements Archiving – SketchesInclude Vehicle-Critical MeasurementsSufficiently detailed to permit a determination of specific vehicle characteristicsDependent 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.
71 Direction of Travel Closely examine tire tracks Using known factors Common sense
72 Direction of Travel Spinning tires Striations by sidewall in furrow Shows which way tire rollingLocation where vehicle stopped, backed up to change directionOverlapping front & rear tire tracksLook to see if coming or going from sceneGrass or small plantsDirection they were flattenedDirectional tire tread patternsDamp soil or snowTires lifted soil or snow slightly in direction of travelDeposition of transferred material in direction of travelMud, dirty water or fluids splashed or thrown in direction of travel
74 Wheelbase Front Tires Turned Defined as the distance between the leading edge of the front and rear tires.Front TireTrack WidthApproximateWheelbaseRear TireTrack WidthFront Tires Turned
75 Wheelbase Front Wheels Turned Inside leading edge of track will be roundedMake rt. Angles to center line of impressionWill run laterally across the width of impressionProject line along inside edge – parallel to center lineIntersection is fixed point on inside leading edgeRepeat of all 4 tires
78 Tilt” of the tires as they CamberTilt” of the tires as theyrest on the ground.Mechanical issues with vehicle affect how impressions appear at sceneDifferences between normal and abnormal camber (positive or negative) signifiesimproper 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 top,Normal CamberNarrowerPositive CamberTire tilted topWiderNegative CamberTire tilted top
80 Front and Rear Track Widths Defined as distance between middle of leading edge of the front and back tires.Mechanical issues can affect how these impressions appear at the scene.Among others, one is camber, which is the “tilt” of the tires as they rest on the ground.
81 Track Width Toe In or Out Difference between front & rear of front tiresNormally set “in” only a few millimetersCompensate for normal front end tendency to toe “out” at highway speeds.Improper alignmentWorn front end components
83 Turning diameterDiameter is defined as the diameter of the circle made when the vehicle is driven in a circle.Determined from measurements scene.
84 Turning Diameter At the scene Procedure Don’t know if the turn is full-lockCurb-to-curb for the outer tiresNot wall-to-wall for outside edge of vehicleProcedureSelect segment reflecting sharpest portion of turnMeasure imaginary line between 2 points of arcMeasure outer margin to outer marginA-AABisect line & draw line to outer margin of track arc –(A-C)Draw another line between the bisect point and the inside of the track arc –(C-B)Calculate diameter
85 Tire circumference Procedure 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-to-accidental characteristic – different from value obtained by wrapping the measuring tape around the tire in its center line,LargerProcedureMeasure distance between repeated accidental characteristics on impressionConsiderationsMeasured value is less than when the tape is wrapped around the tireTires have a curved arc width, impressions do not.Measured circumference is larger in the center line of the tire than at the outer edges.
87 Tread design width (arc 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.
88 Non-dirt Impressions2D impressions visible because of contaminants adhering to the tread; dirt and dust the most common.Other contaminants also create impressionswater, grease (oil) or blood.Each leaves visible impressionEach can be enhanced, depending on the contaminant.Consideration of Enhancement ChoicesVariety of choices and investigators must make the proper decision.Archiving the impression photographically is step-oneEnhancement choices and the variables offered by the scene:Surface material,Chemistry of the impression material (dirt, oil, blood, etc), and theChemistry of the enhancement method.
90 Tread Wear Indicators Tread wear indicators (wear bars) Located in grooves of tread designRun laterally across tread1/16” above base of the grooveUseful for comparison purposesDivide tire into useful segmentsCars & light trucks6 evenly spacedRim diameter of 305mm/12 inches must least 6Less than 305mm must least 3/12 inchesWear Bar Indicator
91 Tread Wear First thousand miles produces the fastest tread wear As elements become shorterFlex less & squirming is reducedSlows considerablyAccidental characteristics last longer on well-worn tire than on a new oneTire wear indicator
93 Measuring Tread Depth Non-Skid Depth Equipment: Tread depth gauge (Measures in 1/32nds) or 15mm rulerNewer tires: 11/32 to 16/32”Maximum depths suggest newer tiresWear bars are 2/32nds,Wear patterns appear as solid bar in the tire impressionProcedureEstimate height of groove in scene impressionSet depth gauge on impression grooveCarefully lower gauge into impression & read depth from the scaleAlternatively, measure depth from cast in dental stone
94 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. …Tire 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.2/32" legally worn out tread depthA 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,
95 Identifying Tread Wear Legally WornExposed tire barsTire bars recessed in sipes & grooves become exposedCircular wearWear around circumference w/sipes & grooves indicates wear4/32 Tread6/32 Tread
97 Enhancing Tire Track Impressions Involves many of the same principles as for footwear evidencePhotography :A method for archiving AND enhancing.Chemical enhancements.Chemical treatments take advantage of the inherent chemical signature of the impressionMinerals, 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.
98 Chemical Enhancement Metals in Soil Impressions with MetalsAmmonium or Potassium ThiocyanateTests for IronReddish brown8-HydroxyquinolineIron, magnesium + other metalsFluorescent under UV lightImpression w/oil or fatsIodine fuming or Iodine crystalsOils & Other organic compoundsIodine absorbedEnhancementBenzophenoneForms stable blue colorThin layer of starch powderSubsequent steam treatment turns starch blue
99 Chemical Enhancement Wet Tires with Salt Deposits - Winter Silver NitrateConverts NaCl (salt) to AgCl (Silver Chloride)NaCl + AgNO AgCl + AgNO3Ag MetalUV or sunlight darkens impressionRoad Salt2% Silver NitrateIn Methanolhv
100 Tire Tracks in Blood Chemical Enhancement Blood reactive chemicalsDABLeucocrystal VioletAcid Violet 17Acid Yellow 7 – dark surfaces – yellow fluorescenceAmido BlackNinhydrinDFOCrowle’s StainTMBCoomassie blueNile RedHungarian RedAshley’s reagent
102 Tire Impressions as Investigational Aids Identifying manufacturer & brand nameDone after processing the sceneTread designWho makes it & whereTire guides – Boca Raton, FLShows 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.
103 On-Scene Information Limited Slip Differential (LSD) Posi-tractionOne wheel was spinningMovie: My Cousin VinnieCan narrow type of vehicleOdd mixture of worn tiresSuggests an older vehiclePossible alignment problemsStolen items - gasolineLocation of gas tankCheck side of car where gas tank locatedEstimate from amount taken whether a truck (pickup-SUV)
108 Age of Tire Impression How Long @ Scene How long an object (driven over) has been lying on the groundComplainant may have this informationTransferred substanceRecently spilled FluidKnocked over objectsWeather conditions prior to offenseHelp date time of deposit of scene impression
110 Known Tire Impressions Need one full circumference of the tireComplex pitch in modern radialsMight miss importantaccidental characteristics
111 Taking Tire Impressions Methods & Materials needed Lg & sm felt marking pensMagnetic jet black print powder3” wide magna brushStrips of polyester plastic 12” x 40” to protect impressionScotch tape to attach plastic to art boardLarge area to make impressionBroomVehicle liftTire marking crayonsRag to clean dirt from tiresRoll of paper towelLarge jar of Petroleum Jelly (Vaseline)GlovesArt board 15” x 40” (3 pieces/tire)
112 Information From Each Tire ID each tire laterManufacturerTire brand nameTire sizeType of tireSummer, etcConstructionRadial, bias ply, etcOther numbersMold, design, etcWearNumber of ribs in designPhotograph TireExterior sidewallTread designSerial numberDesign, mold & drawing numbersShow up after rubbing w/crayon
113 Recording Known Tire Impressions Recording known tire impression Art board is superior to paperSmall debris on surface can’t come throughReduces/eliminates wrinkles/tearing common with paperUse gloves to keep board clean3 pieces of 40” Board sufficient to record 1 full circumference of tireTread Wear Indicators
114 Recording Known Tire Impressions Petroleum Jelly/Magna Brush Method – 2D Place 2 pieces of art board in path of vehicle travelTape on reverse side to hold pieces togetherMark adjoining pieces appropriatelyPush car over recording surfaceVaseline leaves light brown impressionMark on art board as each tread wear indicator (marked on sidewall) rolls byMark spaces on art board to correspond to numbers on known tireTire Wear Indicator MarksPlace locations on sidewall
115 Recording Known Tire Impressions Petroleum Jelly/Magna Brush Method – 2D Cover art board in front & behind impression w/paper towel to protect itClean area of tire that was on the floor when Petroleum Jelly first appliedApply Petroleum Jelly to this area and push car again
116 Recording Known Tire Impressions Vaseline/Magna Brush Method – 2D Near end of second art boardStop vehicleRemove 1st piece of art boardAdd thin coat of Vaseline to tirePlace 3rd piece of art board in path of vehicleContinue pushing until known impression is transferred to this 3rd section
117 Recording Known Tire Impressions Petroleum/Magna Brush Method – 2D Dust impression as soon as possibleWaiting too long causes defined areas of tread to diffuse into art board surfaceBrush with magnetic rt. Angles w/swirling actionAvoid dusting clear areas of boardBlack magnetic Dusting Powder
118 Recording Known Tire Impressions Vaseline/Magna Brush Method – 2D Protecting the impressionCover with clear acetate to prevent smearing or damage during transit & comparison processAllows examiner to draw lines during comparison
119 Recoding Known Tire Impressions Inking Method I Apply ink to art board for 1 full circumferenceFingerprint Ink worksPush car (tire) over inked art boardThis is the inking processPush car over clean strip of white art board to record the impression
120 Recording Known Tire Impressions Inking Method II: Transparent Method Ink the tire as in inking methodDrive tire over transparent acetate or other transparent media (Mylar)Tape to art board - suitable solid backingAdvantagesCan be rolled up for storinglater time for comparisonCan be compared directly to impression when searching for
121 with Acetate Exemplary Overlay Comparing Scene Castwith Acetate Exemplary Overlay
122 Comparing Scene Cast Actual Exemplar Tire The area defined by blue tape isthe segment of the right reartire which corresponds with thecrime scene cast.