types of evidence
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Types of Evidence. Photos from Kendall Hunt Publishing Content from various chapters in Forensic Science for High School Students and numerous other sources. Testimonial evidence is a statement made under oath; also known as direct evidence or prima facie evidence. - PowerPoint PPT PresentationTRANSCRIPT
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Types of Evidence
Photos from Kendall Hunt Publishing
Content from various chapters in Forensic Science for High School Students and numerous other sources
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Classification of EvidenceTestimonial evidence is a statement made under oath;
also known as direct evidence or prima facie evidence.
Physical evidence is any object or material that is relevant in a crime; also known as indirect evidence. Examples are hair, fiber, fingerprints, documents, blood, soil, drugs, toolmarks, impressions, glass.
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Reliability of EyewitnessFactors that affect accuracy:
Nature of the offense and the situation in which the crime is observed
Characteristics of the witnessManner in which the information is retrieved
Additional factors:Witness’s prior relationship with the accusedLength of time between the offense and the
identificationAny prior identification or failure to identify the
defendantAny prior identification of a person other than the
defendant by the eyewitness
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EyewitnessA police composite may be
developed from the witness testimony by a computer program or forensic artist.
FACES—a composite program by InterQuest
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Physical Evidence
Is generally more reliable than testimonial evidence
Can prove that a crime has been committed
Can corroborate or refute testimony
Can link a suspect with a victim or with a crime scene
Can establish the identity of persons associated with a crime
Can allow reconstruction of events of a crime
As a result of the influences on eyewitness memory, physical evidence becomes critical.
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Physical evidence can be used to answer questions about:
What took place at a crime scene
The number of people involved
The sequence of events
Reconstruction
A forensic scientist compares the questioned or unknown sample from the crime scene with a sample of known origin.
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Types of Physical EvidenceTransient evidence is temporary; easily changed or lost; usually observed by
the first officer at the scene.
Pattern evidence is produced by direct contact between a person and an object or between two objects.
Conditional evidence is produced by a specific event or action; important in crime scene reconstruction and in determining the set of circumstances or sequence within a particular event.
Transfer evidence is produced by contact between person(s) and object(s), or between person(s) and person(s).
Associative evidence is something that may associate a victim or suspect with a scene or with each other; e.g., personal belongings.
—Henry C. Lee and Jerry Labriola, Famous Crimes Revisited, 2001
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Examples of Transient EvidenceOdor—putrefaction, perfume, gasoline,
urine, burning, explosives, cigarette or cigar smoke
Temperature—surroundings, car hood, coffee, water in a bathtub, cadaver
Imprints and indentations— footprints, teeth marks in perishable foods, tire marks on certain surfaces
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Examples of Pattern EvidencePattern evidence—mostly in the form of imprints, indentations,
striations, markings, fractures, or deposits
Clothing or article distributionGunpowder residueMaterial damageBody positionToolmarksModus operandi
Blood spatter Glass fracture Fire burn pattern Furniture position Projectile trajectory Tire marks or skid marks
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Examples of Conditional EvidenceLight—headlight, lighting conditions,
lights on or off
Smoke—color, direction of travel, density, odor
Fire—color and direction of the flames, speed of spread, temperature and condition of fire
Location—of injuries or wounds, of bloodstains, of the victim’s vehicle, of weapons or cartridge cases, of broken glass
Vehicles—doors locked or unlocked, windows opened or closed, radio off or on, odometer mileage
Body—position and types of wounds; rigor, livor, and algor mortis
Scene—condition of furniture, doors and windows, any disturbance or signs of a struggle
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Classification of Evidence by NatureBiological—blood, semen, saliva, sweat, tears, hair, bone, tissues, urine, feces,
animal material, insects, bacteria, fungi, botanical material
Chemical—fibers, glass, soil, gunpowder, metals, minerals, narcotics, drugs, paper, ink, cosmetics, paint, plastic, lubricants, fertilizer
Physical—fingerprints, footprints, shoeprints, handwriting, firearms, tire marks, toolmarks, typewriting
Miscellaneous—laundry marks, voice analysis, polygraph, photography, stress evaluation, psycholinguistic analysis, vehicle identification
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Evidence CharacteristicsIndividual—can be identified with a particular person or a single source•Fingerprints - 1 X 1060
• 1 in 1,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000
Blood DNA TypingFingerprints
Class—common to a group of objects or persons
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Class vs. Individual Evidence
The large piece of glass fits exactly to the bottle; it is individual evidence.
These fibers are class evidence; there is no way to determine if they came from this garment.
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Class vs. Individual Evidence, continued
Which examples do you think could be individual evidence?
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Forensic InvestigationsInclude some or all of these seven major activities:
1. Recognition—the ability to distinguish important evidencefrom unrelated material
Pattern recognition
Physical property observation
Information analysis
Field testing
2. Preservation through the collection and proper packaging of evidence
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3. Identification using scientific testing
Physical properties
Chemical properties
Morphological (structural) properties
Biological properties
Immunological properties
4. Comparison of class characteristics measured against those of known standards or controls; if all measurements are equal, then the two samples may be considered to have come from the same source or origin
Forensic Investigations, continued
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5. Individualization in demonstrating that the sample is unique, even among members of the same class
6. Interpretation—giving meaning to all the information
Forensic Investigations, continued
7. Reconstruction of the events in the case Inductive and deductive logic
Statistical data
Pattern analysis
Results of laboratory analysis
—Henry C. Lee and Jerry Labriola, Famous Crimes Revisited, 2001
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Collecting Trace Evidence
Who collects the evidence?
Depends on the state/community
Police Officer Crime Scene Investigator Forensic Scientist
Often one person to ensure consistency of labeling
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Collect trace or entire object?
Suppose a glove appears to have glass, fibers and blood on it.
Should the glass, fibers and blood be removed and packaged separately?
Should the entire glove be packaged?
Trace > Collecting
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Considerations before packaging entire object:
Object may be too large or difficult to move Trace evidence may fall off item during transport. Trace Evidence may be transferred to different,
irrelevant area of object.
If packaging object, package objects separately.
Prevents trace being transferred to other objects.
Trace > Collection
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These 3 methods can be done at the crime scene or in the crime lab.
1. Visual Inspection2. Tape Lift3. Vacuum
Trace > Collection
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Use naked eye or hand lens. Evidence removed and packaged for later
analysis Use bright light and forceps to collect.
Trace > Collection
Visible Inspection
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Small paper envelopes are bad (Holes allow small objects to escape).
Use small plastic bags, glass vial or paper using a druggist fold.
Double package. Label each package.
Trace > Collection
Visible Inspection (Packaging)
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Clear tape is used. Repeatedly apply tape to small area until
most of the stickiness is gone. Tape is folded back upon itself, taped to a
glass slide or taped to a piece of plastic. Put in separate labeled container.
Be sure to document specific area covered.
Trace > Collection
Tape Lift
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Vacuuming
Nozzle should be short and transparent.
Debris is collected on a filter or membrane
Trace > Collection
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Small area is vacuumed. (Filters changed frequently)
Filters packaged in separate labeled container. (Be sure to document specific area covered)
Most improperly used method because it often results in the collection of a lot of irrelevant material.
Vacuuming
Trace > Collection
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Druggist Fold
Consists of folding one end of the paper over one third, then folding the other end one third over that, and repeating the process from the other two sides.
After the paper is folded in this manner, the outside two edges are tucked into each other to produce a closed container that keeps specimen from falling out.
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Wayne Williams Trial
• Fulton County Case in 1981• First case in which primary evidence was
fiber evidence• Fibers linked Williams to being in contact
with the bodies• Media released info that GBI/FBI were
collecting fibers• Williams began dumping nude bodies in
rivers
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Wayne Williams Trial
• Fiber links to dog, cars, home, bedspread• He was convicted for being linked to the
bodies prior to dumping• Set standard for murder trials based on
overwhelming circumstantial evidence
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Hair
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Hair
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IntroductionHuman hair is one of the most frequently found pieces of evidence
at the scene of a violent crime. It can provide a link between the criminal and the crime.
From hair, one can determine:
If the source is human or animal
Race (sometimes)
Origin of the location on the source’s body
Whether the hair was forcibly removed
If the hair has been treated with chemicals
If drugs have been ingested
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Skin Structure
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Hair ShaftComposed of:
Cuticle—outside covering, made of overlapping scales
Cortex—inner layer made of keratin and embedded with pigment; also contains air sacs called cortical fusi
Medulla—inside layer running down the center of the cortex
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The CuticleThe cuticle is the outermost layer of hair which is covered with scales. The scales point toward the tip of the hair. Scales differ among species of animals and are named based on their appearance. The three basic patterns are:
Coronal
Spinous
Imbricate
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Human ScalesIn order to visualize thescales:Paint clear fingernail polish on a
glass slide.
When the polish begins to dry, place a hair on the polish.
When it is almost dry, lift off the hair and observe the scale imprints.
What pattern is seen in this slide?
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The CortexThe cortex gives the hair its shape.It has two major characteristics:
Melanin—pigment granules that give hair its color
Cortical fusi—air spaces, usually found near the root but may be found throughout the hair shaft
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The MedullaThe medulla is the hair core that is not always visible. The medulla comes in different types and patterns.
Types:
Intermittent or interrupted
Fragmented
Continuous
Stacked
Absent—not present
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Human MedullaHuman medulla may be continuous,
fragmented, or absent.
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Medullary IndexDetermined by measuring the diameter of the medulla and dividing it by the diameter of the hair.
Medullary index for human hair is generally less than 1/3.
For animal hair, it is usually greater than 1/2.
mouse
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Hair ShapeCan be straight, curly, or kinky, depending on the cross-section, which may be round, oval, or crescent-shaped.
Round(Straight)
Oval(Curly)
Crescent moon (Kinky)
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Hair GrowthTerminology
Anagen—hair is actively growing; lasts up to 5 years
Catagen—hair is not growing; a resting phase
Telogen—follicle is getting ready to push the hair out; lasts two to six months
Grows about 0.4 mm per day, or 1 cm per month; approximately one-half inch per month
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The RootHuman roots look different based on whether they have been forcibly removed or they are telogen hairs and have fallen out. Animal roots vary, but in general have a spear shape.
Fallen out Forcibly removed
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Hair ComparisonColorLengthDiameterDistribution, shape, and color
intensity of pigment granules
Scale types
Presence or absence of medulla
Medullary type
Medullary pattern
Medullary index• Dyed hair has color in cuticle and cortex
• Bleaching removes pigment and gives a yellow tint
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DNA from HairThe root contains nuclear DNA. If the hair has been forcibly
removed, some follicular tissue containing DNA may be attached.
The hair shaft contains abundant mitochondrial DNA, inherited only from the mother. It can be typed by comparing relatives if no DNA from the body is available. This process is more difficult and more costly than using nuclear DNA.
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Collection of HairQuestioned hairs must be accompanied by an adequate number of
control samples.
• From victim
• From possible suspects
• From others who may have deposited hair at the scene
Control sample
• 50 full-length hairs from all areas of scalp
• 24 full-length pubic hairs
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Hair ToxicologyAdvantages:• Easy to collect and store
• Is externally available
• Can provide information on the individual’s history of drug use or evidence of poisoning
Collections must be taken from different locations on the body to get an accurate timeline.
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Hair Toxicology, continued
Napoleon died in exile in 1821. By analyzing his hair, some investigators suggest he was poisoned by the deliberate administration of arsenic; others suggest that it was vapors from the dyes in the wallpaper that killed him.
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More about HairFor additional information about hair and other trace evidence, check out
truTV’s Crime Library at:
www.crimelibrary.com/criminal_mind/forensics/trace/1.html
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Fibers
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Are considered class evidenceAre considered class evidence
Have probative valueHave probative value
Are common trace evidence at a Are common trace evidence at a crime scenecrime scene
Can be characterized based on Can be characterized based on comparison of both physical and comparison of both physical and chemical properties chemical properties
Fibers
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Fabric
Fabric is made of fibers. Fibers Fabric is made of fibers. Fibers are made of twisted are made of twisted filaments.filaments.
Types of fibers and fabric:Types of fibers and fabric:NaturalNatural——animal, vegetable, animal, vegetable, or inorganicor inorganicArtificialArtificial——synthesized or synthesized or
created from altered created from altered natural sourcesnatural sources
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Types of Fibers
SyntheticSyntheticRayonRayon
NylonNylon
AcetateAcetate
AcrylicAcrylic
SpandexSpandex
PolyesterPolyester
NaturalNatural
SilkSilk
CottonCotton
WoolWool
MohairMohair
CashmereCashmere
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Classification
Natural fibers are classified according to their origin:
Vegetable or cellulose
Animal or protein
Mineral
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Cellulose Fibers
CottonCotton——vegetable fiber; strong, vegetable fiber; strong, tough, flexible, moisture-tough, flexible, moisture-absorbent, not shape-retentiveabsorbent, not shape-retentive
RayonRayon——chemically altered chemically altered cellulose; soft, lustrous, versatilecellulose; soft, lustrous, versatile
Cellulose acetateCellulose acetate——cellulose that is cellulose that is chemically altered to create an chemically altered to create an entirely new compound not found entirely new compound not found in naturein nature
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Fiber Comparison
Can you describe the difference(s) between the cotton onCan you describe the difference(s) between the cotton onthe left and the rayon on the right? the left and the rayon on the right?
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Protein Fibers
WoolWool——animal fiber coming most animal fiber coming most often from sheep, but may be goat often from sheep, but may be goat (mohair), rabbit (angora), camel, (mohair), rabbit (angora), camel, alpaca, llama, or vicuñaalpaca, llama, or vicuña
SilkSilk——insect fiber that is spun by a insect fiber that is spun by a silkworm to make its cocoon; the silkworm to make its cocoon; the fiber reflects light and has fiber reflects light and has insulating propertiesinsulating properties
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Mineral Fibers
AsbestosAsbestos——a natural fiber that has been used in fire-resistant a natural fiber that has been used in fire-resistant substancessubstances
Rock woolRock wool——a manufactured mineral fibera manufactured mineral fiber
FiberglassFiberglass——a manufactured inorganic fibera manufactured inorganic fiber
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Synthetic FibersMade from derivatives of petroleum, coal, and natural gas
NylonNylon——most durable of man-made fibers; extremely lightweightmost durable of man-made fibers; extremely lightweight
PolyesterPolyester——most widely used man-made fibermost widely used man-made fiber
AcrylicAcrylic——provides warmth from a lightweight, soft, and resilient provides warmth from a lightweight, soft, and resilient fiberfiber
SpandexSpandex——extreme elastic propertiesextreme elastic properties
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Fabric Production
Fabrics are composed of individual threads or yarns that are made of Fabrics are composed of individual threads or yarns that are made of fibers and are knitted, woven, bonded, crocheted, felted, knotted, or fibers and are knitted, woven, bonded, crocheted, felted, knotted, or laminated. Most are either woven or knitted. The degree of stretch, laminated. Most are either woven or knitted. The degree of stretch, absorbency, water repellence, softness, and durability are all individual absorbency, water repellence, softness, and durability are all individual qualities of the different fabrics.qualities of the different fabrics.
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Weave Terminology
YarnYarn——a continuous strand of fibers or filaments that may be twisted a continuous strand of fibers or filaments that may be twisted togethertogether
WarpWarp——lengthwise yarnlengthwise yarn
WeftWeft——crosswise yarncrosswise yarn
BlendBlend——a fabric made up of two or a fabric made up of two or more different types of fibersmore different types of fibers
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Weave Patterns
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Plain Weave
The simplest and most common weave The simplest and most common weave patternpattern
The warp and weft yarns pass under The warp and weft yarns pass under each other alternatelyeach other alternately
Design resembles a checkerboardDesign resembles a checkerboard
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Twill Weave
The warp yarn is passed over one The warp yarn is passed over one to three weft yarns before going to three weft yarns before going under one.under one.
Makes a diagonal weave pattern.Makes a diagonal weave pattern.
Design resembles stair steps.Design resembles stair steps.
Denim is one of the most common Denim is one of the most common examples.examples.
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Satin Weave
The yarn interlacing is not uniformThe yarn interlacing is not uniform
Creates long floatsCreates long floats
Interlacing weave passes over four or Interlacing weave passes over four or more yarnsmore yarns
Satin is the most obvious exampleSatin is the most obvious example
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Knitted Fabric
Knitted fabrics are made by Knitted fabrics are made by interlocking loops into a specific interlocking loops into a specific arrangement. It may be one arrangement. It may be one continuous thread or a combination. continuous thread or a combination. Either way, the yarn is formed into Either way, the yarn is formed into successive rows of loops and then successive rows of loops and then drawn through another series of drawn through another series of loops to make the fabric.loops to make the fabric.
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Polymers
Synthetic fibers are made of polymers, which are long chains of Synthetic fibers are made of polymers, which are long chains of repeating chemical units.repeating chemical units.
The word The word polymerpolymer means many ( means many (polypoly) units () units (mermer).).
The repeating units of a polymer are called monomers.The repeating units of a polymer are called monomers.
By varying the chemical structure of the monomers or by varying the By varying the chemical structure of the monomers or by varying the way they are joined together, polymers are created that have way they are joined together, polymers are created that have different properties. different properties.
As a result of these differences, they can be distinguished from one As a result of these differences, they can be distinguished from one another forensically.another forensically.
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Filament Cross Sections
Synthetic fibers are forced out of a nozzle when they are hot, and Synthetic fibers are forced out of a nozzle when they are hot, and then they are woven. The holes of the nozzle are not necessarily then they are woven. The holes of the nozzle are not necessarily round; therefore, the fiber filament may have a unique shape in cross round; therefore, the fiber filament may have a unique shape in cross section.section.
R ound 4-lobed
Octalobal
Irregular
Multi-lobedor Serrate
T rilobal
Dogbone orDumbbell
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Testing for Identification
Microscopic observationMicroscopic observationBurningBurning——observation of how a observation of how a
fiber burns, the odor, color of fiber burns, the odor, color of flame, color of smoke, and the flame, color of smoke, and the appearance of the residueappearance of the residue
Thermal decompositionThermal decomposition——gently gently heating to break down the fiber heating to break down the fiber to the basic monomersto the basic monomers
Chemical testsChemical tests——solubility and solubility and decomposition decomposition
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Testing for Identification
DensityDensity—the —the mass of an object mass of an object divided by the volume of the divided by the volume of the objectobject
Refractive indexRefractive index——measurement measurement of the bending of light as it of the bending of light as it passes from air into a solid or passes from air into a solid or liquidliquid
FluorescenceFluorescence—absorption and —absorption and reemission of light; reemission of light; used for used for comparing fibers as well as comparing fibers as well as spotting fibers for collectionspotting fibers for collection
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Dyes
Components that make up dyes can Components that make up dyes can be separated and matched to an be separated and matched to an unknown.unknown.
There are more than 7,000 different There are more than 7,000 different dye formulations.dye formulations.
Chromatography is used to separate Chromatography is used to separate dyes for comparative analysis.dyes for comparative analysis.
The way a fabric accepts a particular The way a fabric accepts a particular dye may also be used to identify dye may also be used to identify and compare samples.and compare samples.
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Collection of Fiber Evidence
Bag clothing items individually in paper bags. Make sure that different Bag clothing items individually in paper bags. Make sure that different items are not placed on the same surface before being bagged.items are not placed on the same surface before being bagged.
Make tape lifts of exposed skin areas and any inanimate objects.Make tape lifts of exposed skin areas and any inanimate objects.
Removed fibers should be folded into a small sheet of paper and Removed fibers should be folded into a small sheet of paper and stored in a paper bag.stored in a paper bag.
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Fiber Evidence
Fiber evidence in court cases can be Fiber evidence in court cases can be used to connect the suspect to the used to connect the suspect to the victim or to the crime scene. In the victim or to the crime scene. In the case of Wayne Williams, fibers case of Wayne Williams, fibers weighed heavily on the outcome of weighed heavily on the outcome of the case. Williams was convicted in the case. Williams was convicted in 1982 based on carpet fibers that 1982 based on carpet fibers that were found in his home, in his car, were found in his home, in his car, and on several murder victims. and on several murder victims.
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More about Fibers
For additional information about fibers and other trace evidence, check out For additional information about fibers and other trace evidence, check out truTV’s Crime Library at:truTV’s Crime Library at:
www.crimelibrary.com/criminal_mind/forensics/trace/1.htmlwww.crimelibrary.com/criminal_mind/forensics/trace/1.html
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Trace EvidenceTrace evidence is physical evidence
found in small amounts at a crime scene. Common examples would be hair, fiber, paint chips, body fluids, stains, powders, explosive residue, glass particles, vegetative matter, metal particles, and soil. It may also include more unusual types of evidence.
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Physical and Chemical PropertiesPhysical property: A characteristic that does not involve a change in the
identity of a substance, such as odor, color, boiling point, density, refractive index
Chemical property: A characteristic that determines how a substance will change into another substance with different physical properties
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Metal AnalysisBits of metal can be identified from their physical and chemical
properties.
Solid particles—microscopic examination, magnetism, malleability, density, color, solubility, reactivity
Dissolved metals—separation by chromatography with comparison of Rf values to known metals, specific reactions, and color tests
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Analysis of Metal ParticlesA Qualitative Analysis Approach
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Trace Evidence: Qualitative AnalysisWhen investigators find substances at the scene of a crime and send
them to the laboratory for identification, the forensic chemist uses several techniques or lab tests to identify them. One of these techniques is qualitative analysis. For example:
A number of white powders that appear the same can be identified by their physical and chemical properties.
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Qualitative AnalysisMicroscopic Examination
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Qualitative Analysis, continuedCheck for:SolubilitypHChemical reactions
• Color• Precipitate formation• Evolution of gas
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Flame ColorsMany metal salts show a distinct
color when heated.
Sometimes this property can be used in an analysis.
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A Historical CrimeIn 1912, Emile Gourbin was a bank clerk in Lyons, France. He came under
suspicion of strangling his girlfriend, Marie Latelle. Gourbin was arrested but had what appeared to be an airtight alibi. Edmond Locard went to Gourbin’s cell and removed scrapings from under his fingernails. The scrapings contained tissue that possibly came from Marie’s neck, but this was not provable. Locard noticed that the tissue was coated with a pink dust, which he identified as rice starch. On the particles he found bismuth, magnesium stearate, zinc oxide, and a reddish iron oxide pigment called Venetian red. Examination of the face powder used by Marie revealed that a powder prepared for her by a Lyons druggist was similar in composition. In these days of mass-produced face powder, this evidence would have far less significance. However, in 1912, because of the special preparation, it led to the confession of Gourbin.
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A More Recent CrimeA bank robber was startled by an alarm just as the teller handed her
the money. She grabbed it and, in her haste to get away, ran smack-dab into a glass door. Nevertheless, she recovered and got away. Subsequent examination of the door revealed a red lipstick imprint of the perpetrator’s mouth. Police later picked up a suspect, but needed evidence to link her to the robbery. Are lip prints unique enough to tie the suspect to the crime?
http://www.hbo.com/autopsy/episode/episode_6_the_telltale_imprint.html
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Lip PrintsLip prints are different and can be used to identify suspects.
There are several general patterns:
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Chromatography of LipsticksThe lipstick used by the suspect
could also have been compared to the residue on the door.
Thin-layer chromatography (TLC) can be used to separate the components of a lipstick. The chromatograms can then be compared for a possible match.
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PaintPaint can be used as evidence in hit-
and-run cases.
The layers of different paints in a cross section may be unique.
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Soil and Glass Analysis
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You will be able to:You will be able to:Make density measurements Make density measurements
on very small particles. on very small particles. Use logic to reconstruct Use logic to reconstruct
events. events. Use technology and Use technology and
mathematics to improve mathematics to improve investigations and investigations and communications. communications.
Identify questions and Identify questions and concepts that guide concepts that guide scientific investigations.scientific investigations.
Objectives, continued
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The legal application of earth and soil scienceCharacterization of earthen materials that have been transferred
between objects or locations and the analysis of possible origin or sources
Forensic Geology
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Forensic Geologist Tools
Binocular microscopes
Petrographic microscopes
X-ray diffraction
Scanning electron microscopes
Microchemical analysis
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Forensic Geology History
1887–1893—Sir Arthur Conan Doyle wrote about scientific ideas and techniques for solving crimes in his writings of Sherlock Holmes. This included information about soil and its composition which had never actually been used.
1893—An Austrian criminal investigator, Hans Gross, wrote that there should be a study of “dust, dirt on shoes and spots on cloth.” He observed, “Dirt on shoes can often tell us more about where the wearer of those shoes had last been than toilsome inquiries.”
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Forensic Geology History, continued
1904—Georg Popp, a German forensic scientist, presented the first example of earth materials used as evidence in a criminal case, the strangulation of Eva Disch.
1910—Edmond Locard, a forensic geologist, was most interested in the fact that dust was transferred from the crime scene to the criminal. This helped to establish his principle of transfer.
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Soil
A. Definition—naturally deposited materials that cover the earth’s surface and are capable of supporting plant growth
B. The Earth
• 75 percent—oceans, seas, and lakes• 15 percent—deserts, polar ice caps, and mountains• 10 percent—suitable for agriculture
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Soil, continued
C. Formation
• Living matter—plants, animals, microorganisms
• Inorganic materials
• Climate
• Parent materials
• Relief—slope and land form
• Time
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Soil, continued
D. Profile E. Composition
• Topsoil
• Subsoil
• Parent material
• Sand
• Silt
• Clay
• Organic matter
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Soil, continued
F. Nutrients—macro G. Nutrients—micro
• Nitrogen
• Phosphorus
• Potassium
• Calcium
• Magnesium
• Sulfur
• Manganese
• Iron
• Boron
• Copper
• Zinc
• Molybdenum
• Chlorine
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Soil Comparisons
May establish a relationship or link to the crime, the victim, or the suspect(s)
Physical properties—density, magnetism, particle size, mineralogy
Chemical properties—pH, trace elements
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Probative Value of Soil
Types of earth material are virtually unlimited. They have a wide distribution and change over short distances.
As a result, the statistical probability of a given sample having properties the same as another is very small.
Evidential value of soil can be excellent.
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Increasing Probative Value
Rare or unusual minerals
Rocks
Fossils
Manufactured particles
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Minerals
More than 2,000 have been identified.Twenty or so are commonly found in
soils; most soil samples contain only three to five.
Characteristics for identification—size, density, color, luster, fracture, streak, magnetism
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Rocks
Aggregates of mineralsTypes• Natural—like granite• Man-made—like concrete
Formation• Igneous• Sedimentary• Metamorphic
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Palynology
The study of pollen and sporesImportant to know:
What is produced in a given area The dispersal pattern
Variation in size and weight
For additional information about palynology, visit:
http://science.uniserve.edu.au/faces/milne/milne.html
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Soil Evidence
Class characteristics—the type of soil may have similar characteristics at the primary and/or secondary crime scene, on the suspect or on the victim
Individual characteristics—only if the soil has an unusual or specialized ingredient such as pollen, seeds, vegetation, or fragments
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Sand
Sand is the term applied to natural particles with a grain diameter between 1/16 mm and 2 mm.
Its color and contents are dependent upon the parent rock and surrounding plant and animal life.
(The photo on the right shows color differences in sand from six locations around the world.)
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Sand Characteristics
Composition is based on the material of the source; also gives the sand its color
Texture is determined by the way the source was transported• Shape
• Grain size
• Sorting
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Forensic Geology in the News
A nine-year-old’s body was found in a wooded area along a river in Lincoln County, South Dakota. A forensic geologist collected soil samples from the fenders of a suspect’s truck and from the area where the body was found. Both soils contained grains of a blue mineral that turned out to be gahnite, a rare mineral that had never been reported in South Dakota. As a result, the soil tied the suspect to the crime.
Check out other cases at: www.forensicgeology/science.htm
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Characteristics of Glass
Hard, amorphous solid
Usually transparent
Primarily composed of silica, with various amounts of elemental oxides
Brittle
Exhibits conchoidal fracture
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Soda-lime—used in plate and window glass, glass containers, and electric lightbulbs
Soda-lead—fine tableware and art objects
Borosilicate—heat-resistant, like Pyrex
Silica—used in chemical ware
Tempered—used in side windows of cars
Laminated—used in the windshield of most cars
Common Types
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Density—mass divided by volume
Refractive index (RI)—the measure of light bending due to a change in velocity when traveling from one medium to another
Fractures
Color
Thickness
Fluorescence
Markings—striations, dimples, etc.
Physical Characteristics
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Density
Type of Glass Density
window 2.46–2.49
headlight 2.47–2.63
Pyrex 2.23–2.36
lead glass 2.9–5.9
porcelain 2.3–2.5
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Determination of Refractive Index
Immersion method—lower fragments into liquids whose refractive index is different
Match point—when the refractive index of the glass is equal to that of the liquid
Becke line—a halo-like glow that appears around an object immersed in a liquid. It disappears when the refractive index of the liquid matches the refractive index of the object (the match point).
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Determination of Refractive Index, continued
The refractive index of a high-boiling liquid, usually a silicone oil, changes with temperature.
This occurs in an apparatus called a hot stage which is attached to a microscope. Increasing the temperature allows the disappearance of the Becke line to be observed.
At match point, temperature is noted and refractive index of the liquid is read from a calibration chart.
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The Becke Line
The Becke line is a “halo” that can be seen on the inside of the glass on the left, indicating that the glass has a higher refractive index than the liquid medium. The Becke line as seen on the right is on the outside of the glass, indicating just the opposite.
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Refractive Index
Liquid RI Glass RIWater 1.333 Vitreous silica 1.458
Olive oil 1.467 Headlight 1.47–1.49
Glycerin 1.473 Window 1.51–1.52
Castor oil 1.482 Bottle 1.51–1.52
Clove oil 1.543 Optical 1.52–1.53
Bromobenzene 1.560 Quartz 1.544–1.553
Bromoform 1.597 Lead 1.56–1.61
Cinnamon oil 1.619 Diamond 2.419
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Fracture Patterns
Radial fracture lines radiate out from the origin of the impact; they begin on the opposite side of the force.
Concentric fracture lines are circular lines around the point of impact; they begin on the same side as the force.
3R rule—Radial cracks form a right angle on the reverse side of the force.
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Sequencing
A high-velocity projectile always leaves a wider hole at the exit side of the glass.
Cracks terminate at intersections with others. This can be used to determine the order in which the fractures occurred.
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Glass as Evidence
Class characteristics: physical and chemical properties such as refractive index, density, color, chemical composition
Individual characteristics: if the fragments can fit together like pieces of a puzzle, the source can be considered unique
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Considerations for Collection
The collector must consider that fragments within a questioned sample may have multiple origins. If possible, the collector should attempt an initial separation based on physical properties.
The collector must consider the possibility that there may be a physical match to a known sample (e.g., a piece of glass to a fractured vehicle headlamp). When an attempt to make a physical match is made at the site of collection, the collector should take precautions to avoid mixing of the known and questioned samples.
Any glass samples collected should be documented, marked (if necessary), packaged, and labeled.
—Forensic Science Communications
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Collecting the SampleThe glass sample should consist of the largest amount that can be
practically collected from each broken object and packaged separately. The sample should be removed from the structure (e.g., window frame, light assembly). The inside and outside surfaces of the known sample should be labeled if a determination of direction of breakage or reconstruction of the pane is desired.
When multiple broken glass sources are identified, it is necessary to sample all sources.
A sample should be collected from various locations throughout the broken portion of the object in order to be as representative as possible.
The sample should be collected with consideration being given to the presence of other types of evidence on that sample (e.g., fibers, blood).
—Forensic Science Communications