Physical EvidencePhysical Evidence

Forensic FuelForensic Fuel

Chapter 3Chapter 3

Lecture HighlightsLecture Highlights

Negative ControlsNegative Controls Comparison and IdentificationComparison and Identification Class vs. Individual CharacteristicsClass vs. Individual Characteristics

Crime SceneCrime Scene

In most cases access to the crime scene In most cases access to the crime scene lasts for about 4 hourslasts for about 4 hours

Can’t collect everything!Can’t collect everything! Want to collect evidence that is likely toWant to collect evidence that is likely to

– Determine Determine What happenedWhat happened What was usedWhat was used How it happenedHow it happened Who did whatWho did what

Rely on logic, common sense, experience, Rely on logic, common sense, experience, and knowledge of forensic capabilitiesand knowledge of forensic capabilities– Every scene is differentEvery scene is different

Types of Physical EvidenceTypes of Physical Evidence Body FluidsBody Fluids

– Blood, semen, salivaBlood, semen, saliva DocumentsDocuments DrugsDrugs ExplosivesExplosives FibersFibers FingerprintsFingerprints Guns & AmmoGuns & Ammo GlassGlass HairHair ImpressionsImpressions

• Paint• Gas, paint thinner• Plastic bags• Powder residues• Serial nos.• Soil• Tool marks• Vehicle lights• Wood• Clothing• Etc.

Analysis of physical evidence Analysis of physical evidence serves 2 purposesserves 2 purposes

IdentificationIdentification– Determine the physical or chemical identity of a Determine the physical or chemical identity of a

substancesubstance– Is it really heroin?Is it really heroin?

ComparisonComparison– Determining whether two objects have a similar Determining whether two objects have a similar

originorigin– Is Hair from same person?Is Hair from same person?– Is paint chip from that car?Is paint chip from that car?

IdentificationIdentification

How do you determine the identity of a How do you determine the identity of a substance?substance?– Test itTest it

Heroine MethamphetamineSample

Marquis Test

When can you be sure?When can you be sure?

Identification requires that you are able to Identification requires that you are able to exclude all other possibilitiesexclude all other possibilities– Could any other compound turn the Marquis Could any other compound turn the Marquis

reagent orange?reagent orange? YesYes Therefore this test alone in not conclusive (definitive)Therefore this test alone in not conclusive (definitive) Can combine several tests to reach a definite Can combine several tests to reach a definite

conclusion regarding IDconclusion regarding ID

Negative ControlNegative Control

When sample is attached to some materialWhen sample is attached to some material– Like clothing, sheets, carpet, auto seat, etc.Like clothing, sheets, carpet, auto seat, etc.

Need to collect a negative controlNeed to collect a negative control– A sample of the same material without evidence on itA sample of the same material without evidence on it

Bloody carpetBloody carpet– 1 cut of carpet with blood1 cut of carpet with blood

– 1 cut of same carpet without blood1 cut of same carpet without blood

ComparisonComparison

Determine whether two samples come from Determine whether two samples come from the same originthe same origin– Did the hair found at the crime scene come from Did the hair found at the crime scene come from

the suspect?the suspect?– Did the carpet fiber found on the victim come Did the carpet fiber found on the victim come

from the suspects apartment?from the suspects apartment?– Did the blood found on the broken window Did the blood found on the broken window

come from the suspect?come from the suspect?

Comparison of glassComparison of glass

Select properties of the evidence to compareSelect properties of the evidence to compare– Puzzle fit, color, thickness, density, RIPuzzle fit, color, thickness, density, RI

Compare these propertiesCompare these properties

Assess the likelihood (probability) that these Assess the likelihood (probability) that these sample came from the same originsample came from the same origin

Comparison of HairComparison of Hair

Rabbit Hair frombox in which victim was found

Rabbit Hair fromsuspect’s coat

Choose Properties

DiameterColorCuticle StructureMedula

STR DNA comparisonSTR DNA comparison

Choose Properties

Size of DNA fragments

Individual vs. Class Individual vs. Class CharacteristicsCharacteristics

Individual CharacteristicsIndividual Characteristics– Evidence that can be associated with a Evidence that can be associated with a

common source with a high degree of common source with a high degree of probabilityprobability

Class CharacteristicsClass Characteristics– Associated only with a groupAssociated only with a group– Not with a single sourceNot with a single source

Class or Individual?Class or Individual? Fingerprint characteristicsFingerprint characteristics

– IndividualIndividual Blood Type (A, B, AB, O)Blood Type (A, B, AB, O)

– ClassClass Automobile paint chip (year, model, color)Automobile paint chip (year, model, color)

– ClassClass Wear patterns on footwear or tiresWear patterns on footwear or tires

– IndividualIndividual DNADNA

– IndividualIndividual Fibers from carpet or clothingFibers from carpet or clothing

– ClassClass Matching tool marks, striationsMatching tool marks, striations

– IndividualIndividual

Class CharacteristicsClass Characteristics

ImportantImportant– Even though circumstantialEven though circumstantial

Support the theorySupport the theory– Enough class evidence can be very compellingEnough class evidence can be very compelling

Enough to exonerate innocent suspectsEnough to exonerate innocent suspects– Victim’s blood is type OVictim’s blood is type O– Suspect’s blood is type ASuspect’s blood is type A– Blood found at scene is type ABBlood found at scene is type AB

Collection of Physical EvidenceCollection of Physical Evidence

FibersFibers HairHair GlassGlass Flammable LiquidsFlammable Liquids BloodBlood Controlled SubstancesControlled Substances Latent FingerprintsLatent Fingerprints Tool MarksTool Marks PaintPaint

Evidence CollectionEvidence Collection

Collection of FibersCollection of Fibers

Pick up with fingers of forcepsPick up with fingers of forceps Place in a paper bindle – druggist foldPlace in a paper bindle – druggist fold Place folded paper in coin envelopePlace folded paper in coin envelope

– Do not place loose fibers in envelopeDo not place loose fibers in envelope– Could get lostCould get lost

Entire garment of cloth itemEntire garment of cloth item If fibers are attached to object – collect the objectIf fibers are attached to object – collect the object

GlassGlass

Glass from different locations is kept in separate Glass from different locations is kept in separate containerscontainers

Place small fragments in plastic containersPlace small fragments in plastic containers Large pieces placed in boxes separated with Large pieces placed in boxes separated with

cotton or tissue to prevent breakagecotton or tissue to prevent breakage

Comparison pieces from window, headlight, bottle, Comparison pieces from window, headlight, bottle, etc.etc.

Flammable LiquidsFlammable Liquids

Clean glass vial with airtight sealClean glass vial with airtight seal– Avoid rubber seal or plastic containerAvoid rubber seal or plastic container

Small samples of soil, wood, cloth, paper should Small samples of soil, wood, cloth, paper should be placed in small clean metal cansbe placed in small clean metal cans– Prevent loss of volatile componentsPrevent loss of volatile components

Larger items (wood, upolstry, wallboard) can be Larger items (wood, upolstry, wallboard) can be heat sealed in KAPAK plasticheat sealed in KAPAK plastic

BloodBlood

Liquid PoolLiquid Pool– Absorb on clean, sterile gauzeAbsorb on clean, sterile gauze– Dry at room tempDry at room temp– Refrigerate or FreezeRefrigerate or Freeze

Dried Blood StainDried Blood Stain– If on clothing package entire article in brown paper If on clothing package entire article in brown paper

bagbag– Small item Small item – Large itemLarge item

Scrape into druggists fold, seal in envelopeScrape into druggists fold, seal in envelope Moisten sterile swab, rub stain, dry, packageMoisten sterile swab, rub stain, dry, package

Maintain Chain of CustodyMaintain Chain of Custody

Log of what happened to Log of what happened to evidence from the time it evidence from the time it was collected to the time was collected to the time it appears in courtit appears in court