2 How can an impression be used to solve a crime? Essential Question:How can an impression be used to solve a crime?
3 ImpressionsAn object or surface takes the form of another through direct contact.Two types:2 dimensional: transfer of an imprint to a firm substrate (glass, paper, floors, etc.)EX: lip print on a glass window3 dimensional: transfer of an imprint to a soft substrate (mud, grass, snow, etc.; usually outdoors)EX: footprint in mudSubstrate: the surface/object/organism/enzyme being effected2D examples: usually found indoors on surfaces like counter tops, glass, paper, cardboard, ceramic floors and waxed floors-fingerprint-black tire tread mark on a paved road3D examples: usually found outdoors in mud, sand, grass, dirt, clay, tar, or snow-tire mark in the dirt-a bite mark on your arm
4 Reasons for examining impressions: it is evidence! May prove that a crime has been committedEstablish key elements of a crimeLink a suspect with a crime scene or a victimEstablish the identity of a victim or suspectCorroborate verbal witness testimonyExonerate the innocentGive detectives leads to work within the case
5 Ways to Recover Impressions: Mechanical processing:Brush and Powder methodTape liftUsed for 2D impressionsEx: footprints on a waxed floorCasting:Making a replica of the impressionFilling a 3D form with a material mold that will not destroy the impressionUsed for 3D impressionsEx: Tool marks on a window sill or tire impression in the mudElectrostatic Lifting:A charge is used to lift dry materials from the surface to a black filmEx: Shoe impression on a dusty floorOblique angle photography:method of documenting impressionsImpressions in dust are obviously extremely delicate, though can be carefully recovered using electrostatic treatment. An electrostatic lifter passes a voltage across a thin layer of conductive film, which is composed of a lower layer of black insulating plastic with an upper layer of aluminium foil. The electrostatic charges cause particles of the impressions to jump onto the black underside, recovering the dust impression
6 Ways to Enhance Impressions: Dyes:Used on glass or marble surfacesLuminol:Chemical with luminescent properties activated upon contact with the iron in bloodEx: may be applied to enhance a bloody footprintAlternative light:Used on porous surfaces like wood or paperEx: Black lightDusting:Powder and brush
7 Think: Individually answer this question: Which technique for collecting impressions would be best for lifting bite marks from a victim? Explain.You have 2 mins!
8 Do you both agree on the same technique? Pair & Share:Discuss your answer with a partnerDo you both agree on the same technique?You have 2 mins!
9 Types of Impressions: Foot impressions Bite marks Tire impressions Tool marks
10 Bite Marks Can be as complex as a fingerprint Individual evidenceDental records & X-rays are often used to identify individualsShow position of teeth, fillings, etc.What they may tell you:Can identify a suspect or victimMost often indicate assault or sexual attackAre common with domestic violenceDental xrays: show position of teeth, fillings, wear…
11 Bite Marks 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 testsTeeth are one of the hardest substances in the human body, so they are frequently well preserved.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.
12 Bite Marks Age determination Milk teeth present: generally under 12 Wisdom teeth present: yrs old
13 Shoe Impressions The most commonly missed evidence at a crime scene Class characteristics:SizeManufacturerModelTypeIndividual characteristics:Gait-manner of moving the footWear of shoes, esp. outsolesOutsoles: outer soles of shoes at bottomDamagecuts, gouges, chunks…debrisnails/screwsShoeprint databases usedex: SloMate and TreadMarkLength of stride and the way the footprint digs in the ground can suggest runningwear - the gradual erosion of rubber due to frictional forces
14 Shoe Impressions What they tell you: Number of suspects Corroborate or dispute alibis and witness testimonyCan link two crimesLink a suspect to a victim or crime scenePoint of entry/exitPosition of the suspect, victim, and/or witnessPathway through the crime sceneDirection of travelTime period (from temporary impressions such as in snow or dew)Also tell you the sequence and manner (walking, running, limping, staggering) in which the impressions were created.
15 Shoe Impressions What they tell you continued: Size: approximate height of an individualPut heel to wall and measure left foot from wall to tip of the big toe.The length of an adult’s foot is about 15% of his/her heightThis percentage varies in growing individuals
16 Shoe Impressions Features to analyze: Tread patterns, size, and depth Wear patterns caused by the way a person walksMaterial defects or damage (nicks, cuts, etc.)Other trace materials, such as soil, tar, rocks, and paint that would indicate where a person has been
17 Ticket to leaveOn a sheet of paper, WRITE THE QUESTION & ANSWER to these true or false questions:1. T or F. Impressions are the most apparent pieces of evidence at a crime scene2. T or F. There are two types of impressions:2D and 3D impressions.3. T or F. Casting can be used to lift a shoe impression in the dirt4. T or F. Approximate age is determined through bite marks.5. T or F. Bite marks are individual evidence.
18 Tire Impressions What they tell you: Type of tire Make or model of the tireDirection of travel after and/or before the crimeNumber of vehicles presentMay eliminate a suspected tireMatch a tire to a suspect
19 Tire Impressions Features to analyze: Wheelbase Stance = Track width Distance between the center of the front tire and the center of the back tire.Stance = Track widthDistance between the two front tires or the two back tiresClass characteristicsEx: size, tread designIndividual characteristicsEx: Cuts, gouges, wear,debris (rocks, nails)individual characteristics can be used to identify an exact tire.individual characteristics change over timeCuts, Gouges, Chunks, Etc.Specific Wear DetailsRock or Other Debris HoldsNails/ScrewsClass Characteristics can be used to eliminate a suspected tire or suggest a tire could have made the track.SizeTread DesignNoise TreatmentMold VariationsOverall Wear
20 Tool Marks Types of Tool Marks: Compression: substrate caught between two opposing forces (pinching or shearing marks)Wrench, pliersSliding: a tool scrapes across a substrate causing parallel striationsScrewdriver
21 Tool Marks What they tell you: Type of tool used Size and shape of the tool used (class characteristics)Rule out suspected toolsShape and pattern of imperfections (individual characteristics)Can be matched to tools in suspect’s possessionEntry/exit to crime scene
22 Tool Marks How are tool mark impressions collected? Pictures of tool markCasting using plaster or siliconeCollecting by castingNever put comparison tools in original toolmark
23 Admissibility of Evidence Probative value3 standards:RelevanceProves or disproves a fact of the crimeCompetenceReliability of the evidenceMateriality of evidenceProves an essential fact of the caseRelevance ex: A tool stained with a suspect's blood might be relevant, for example, but so is the person who sold that tool to the suspect. However, testimony from a toddler discussing a broken house contract would be deemed irrelevant and therefore inadmissible because a child would be too young to understand the case.Competence ex: matching fingerprints, the results of a DNA test, or an expert on footwear impressionsMaterial ex: if a lawyer attempts to prove that the drapes in the room of a murder scene were blue, chances are a judge will deem such evidence immaterial. The room itself may be relevant to the case, but it's likely the color of the drapes doesn't have anything to do with the murder.
24 Georgia Performance Standard SFS1. Students will recognize and classify various types of evidence in relation to the definition and scope of Forensic Science.d. Evaluate the relevance of possible evidence at the site of an investigation.SFS4 Students will evaluate the role of ballistics, tool marks and evidence of arson in forensic investigation.c. Recognize the forensic significance of tool marks, footwear and tire impressions in an investigation.
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