Chapter 3 – Physical Evidence List the common types of physical evidence encountered at crime scenes List the common types of physical evidence encountered

Chapter 3 – Physical Chapter 3 – Physical EvidenceEvidence

List the common types of physical evidence List the common types of physical evidence encountered at crime scenesencountered at crime scenes

Explain the difference between the Explain the difference between the identification and comparison of physical identification and comparison of physical evidenceevidence

Define individual and class characteristicsDefine individual and class characteristics Discuss the value of class evidence to a Discuss the value of class evidence to a

criminal investigationcriminal investigation Explain the purpose physical evidence plays Explain the purpose physical evidence plays

in reconstructing the events surrounding in reconstructing the events surrounding the commission of the crime scene.the commission of the crime scene.

Common Types of Physical Common Types of Physical EvidenceEvidence

1.1. Blood, semen, and saliva - identity Blood, semen, and saliva - identity and possible originand possible origin

a.a. Liquid or driedLiquid or driedb.b. Human or AnimalHuman or Animal

2.2. Documents – authenticity or sourceDocuments – authenticity or sourcea.a. Handwriting Handwriting b.b. TypewritingTypewriting

3.3. Drugs – Drugs – a.a. Any seized substanceAny seized substance


4.4. ExplosivesExplosivesa.a. Devices containing explosive chargeDevices containing explosive chargeb.b. Objects suspected to contain residues of Objects suspected to contain residues of

explosiveexplosive

5.5. Fibers – transfers establish Fibers – transfers establish relationshipsrelationships

a.a. NaturalNaturalb.b. SyntheticSynthetic

6.6. FingerprintsFingerprintsa.a. LatentLatentb.b. VisibleVisible


7.7. Firearms & AmmunitionFirearms & Ammunitiona.a. FirearmFirearmb.b. Discharged or intact ammunitionDischarged or intact ammunition

8.8. GlassGlassa.a. Glass particle or fragmentGlass particle or fragmentb.b. Windowpanes w/ holes made by bulletWindowpanes w/ holes made by bullet

9.9. HairHaira.a. AnimalAnimalb.b. humanhuman


10.10. ImpressionsImpressionsa.a. Tire markingsTire markingsb.b. Shoe printsShoe printsc.c. Depressions in soft soilsDepressions in soft soilsd.d. Glove, fabric impressionsGlove, fabric impressionse.e. Bitemarks in skin, foodBitemarks in skin, food

11.11. Organs and physiological fluidOrgans and physiological fluida.a. Test existence of drugs or poisonsTest existence of drugs or poisonsb.b. Blood analyzed for alcohol or drugsBlood analyzed for alcohol or drugs

12.12. PaintPainta.a. Liquid or driedLiquid or driedb.b. Transferred from one surface to anotherTransferred from one surface to another


13.13. Petroleum productsPetroleum productsa.a. Gasoline – residues from arsonGasoline – residues from arson

b.b. Grease and oil stainsGrease and oil stains

14.14. Plastic BagsPlastic Bagsa.a. Polyethelene disposable bagsPolyethelene disposable bags

15.15. Plastic, rubber, other polymersPlastic, rubber, other polymersa.a. Remnants of man-made materialsRemnants of man-made materials

16.16. Powder ResiduesPowder Residuesa.a. Item suspected of containing firearm Item suspected of containing firearm

discharge residuesdischarge residues


17.17. Serial numbersSerial numbersa.a. Stolen property for restoration of erased I.D. #Stolen property for restoration of erased I.D. #

18.18. Soil and MineralsSoil and Mineralsa.a. Imbedded in shoesImbedded in shoes

b.b. Safe insulation in garmentsSafe insulation in garments

19.19. Tool MarksTool Marksa.a. Screwdriver or crowbar impressed into Screwdriver or crowbar impressed into

another objectanother object

20.20. Vehicle LightsVehicle Lightsa.a. Light on or off at time of impactLight on or off at time of impact


21.21. Wood & other vegetative matterWood & other vegetative mattera.a. WoodWood

b.b. SawdustSawdust

c.c. ShavingsShavings

d.d. Vegetative matterVegetative matter

e.e. On shoes, clothing, or toolsOn shoes, clothing, or tools

IdentificationIdentification

Ultimate Goal in identifying a specific Ultimate Goal in identifying a specific physical or chemical substance is exclude physical or chemical substance is exclude other substancesother substances

1.1. Requires adoption of testing procedures that Requires adoption of testing procedures that have characteristic results for specific have characteristic results for specific standard materialsstandard materials

a.a. Once established, procedure can be used repeatedly Once established, procedure can be used repeatedly to prove identityto prove identity

2.2. Requires that # and type of tests needed to Requires that # and type of tests needed to identify a substance be:identify a substance be:

a.a. Sufficient to exclude all other substancesSufficient to exclude all other substances

b.b. I.E. eliminate all but one substanceI.E. eliminate all but one substance


Determination of physical or chemical Determination of physical or chemical identity of a substance with as near identity of a substance with as near absolute certainty as possibleabsolute certainty as possible Illicit drug preperation – heroin, cocaine, Illicit drug preperation – heroin, cocaine,

barbituratesbarbiturates Gasoline residue from debris of a fireGasoline residue from debris of a fire Nature of explosive residues – dynamite or Nature of explosive residues – dynamite or

TNTTNT Species of Origin – blood, semen, hair, Species of Origin – blood, semen, hair,

woodwood


3.3. Each type of evidence requires a Each type of evidence requires a different test; each test has a different different test; each test has a different degree of specificitydegree of specificity

a.a. Substance A – one testSubstance A – one test

b.b. Substance B – 5 or 6 testsSubstance B – 5 or 6 tests

c.c. No control over quality or quantity of No control over quality or quantity of specimensspecimens

d.d. Forensic scientist determines at what Forensic scientist determines at what point analysis is concludedpoint analysis is concluded

e.e. Has to be beyond reasonable doubt for Has to be beyond reasonable doubt for court of lawcourt of law

ComparisonComparison

Suspect specimen and a Suspect specimen and a standard/reference specimen run standard/reference specimen run through same tests, examinations to through same tests, examinations to determine common origindetermine common origin Hairs at crime scene to hairs in suspect Hairs at crime scene to hairs in suspect

headhead Paint chip from victim’s clothing to car Paint chip from victim’s clothing to car

in hit-and-runin hit-and-run


Procedure:Procedure:1.1. Combinations of select properties chosen Combinations of select properties chosen

from suspect and standard/reference samplefrom suspect and standard/reference samplea.a. Which properties and how many properties Which properties and how many properties

depends on type of material (more details later….)depends on type of material (more details later….)

2.2. Once testing complete, forensic scientist Once testing complete, forensic scientist concludes on origins of specimenconcludes on origins of specimen

a.a. One or more properties doesn’t agree – not same One or more properties doesn’t agree – not same originorigin

b.b. All properties agree – is it always the same origin?All properties agree – is it always the same origin?


Not necessarily always the sameNot necessarily always the same Evidential value – probability in Evidential value – probability in

ascertaining origins of two or more ascertaining origins of two or more specimensspecimens

Probability Probability a.a. Frequency of occurrence of an eventFrequency of occurrence of an event

b.b. Odds at which a certain event will occurOdds at which a certain event will occur

What does this mean?What does this mean? Variation of characteristics of each Variation of characteristics of each

specimen need to be taken into accountspecimen need to be taken into account Individual vs. Class CharacteristicsIndividual vs. Class Characteristics

Class CharacteristicsClass Characteristics

The properties that all the members The properties that all the members of a certain group of objects or of a certain group of objects or substances have in commonsubstances have in common

Frequent problem: inability of lab to Frequent problem: inability of lab to relate physical evidence to a relate physical evidence to a common origin with a high degree of common origin with a high degree of certaintycertainty

Probability is a determining factorProbability is a determining factor

Class CharacteristicsClass Characteristics Initial categories are broad and then narrowed Initial categories are broad and then narrowed

down as more information is obtaineddown as more information is obtained ExampleExample

Blue substanceBlue substance Blue paintBlue paint Blue car paintBlue car paint Blue car paint from Ford Manufacturing Blue car paint from Ford Manufacturing

CompanyCompany Blue car paint from Ford produced 1998-Blue car paint from Ford produced 1998-

20002000 Blue car paint from Ford produced 1998-Blue car paint from Ford produced 1998-

2000, used on Mustang and Explorer2000, used on Mustang and Explorer


The previous “paint” example was a The previous “paint” example was a refined class evidence identificationrefined class evidence identification

The “paint” was identified by The “paint” was identified by comparing its class characteristics comparing its class characteristics with those of known standards or with those of known standards or previously established criteria. previously established criteria.

The “paint” is considered CLASS The “paint” is considered CLASS EVIDENCEEVIDENCE

Other Examples…Other Examples…

Single layered Single layered paint paint

SoilSoil Glass fragments Glass fragments

too small to fit too small to fit back togetherback together

HairsHairs FibersFibers


ProbabilityProbability Two paint chips with one layer of Two paint chips with one layer of

similar colorsimilar color Two paint chips with 7 similar paint Two paint chips with 7 similar paint

layers, not all part of car’s original colorlayers, not all part of car’s original color Which has high probability of same Which has high probability of same

origin?origin?


Blood – 2 samples, both human Blood – 2 samples, both human origin, both type Aorigin, both type A Type A is 26% occurrence in population Type A is 26% occurrence in population

– not enough for comparison -BUT-– not enough for comparison -BUT- Use more blood factors to compare – Use more blood factors to compare –

probability increasesprobability increases Blood proteins, growth factors, clotting Blood proteins, growth factors, clotting

factors, enzymesfactors, enzymes


Product Rule Product Rule – calculates overall – calculates overall frequency of occurrence in a frequency of occurrence in a populationpopulation Factor A % occurrence * Factor B % Factor A % occurrence * Factor B %

occurrence= probability that both occurrence= probability that both events will occur simultaneouslyevents will occur simultaneously

Applies when using factors that occur Applies when using factors that occur independently of one anotherindependently of one another


Product Rule Example:Product Rule Example:Blood FactorsBlood Factors FrequencyFrequency

AA 26% 26%

EsD1EsD1 85% 85%

PGM2+2-PGM2+2- 2% 2% Multipy (.26) (.85) (.02)= .44% or 1 in 200 Multipy (.26) (.85) (.02)= .44% or 1 in 200 Probability that a blood sample will Probability that a blood sample will

contain all three types - .44% or 1 in 200 contain all three types - .44% or 1 in 200 peoplepeople

Value of Class EvidenceValue of Class Evidence

Many lawyers try to discredit class evidence Many lawyers try to discredit class evidence because it cannot be limited to just one because it cannot be limited to just one possible source possible source

However Class Evidence DOES HAVE VALUE. However Class Evidence DOES HAVE VALUE. Look around room, most have different Look around room, most have different

clothes on. If I were to pick a fiber from one clothes on. If I were to pick a fiber from one persons clothes in this room, that fiber could persons clothes in this room, that fiber could possibly pick out the single source or at least possibly pick out the single source or at least narrow the fieldnarrow the field

Some class evidence holds little forensic value Some class evidence holds little forensic value such as fiber from jeans or white cotton such as fiber from jeans or white cotton shirts…they are too commonshirts…they are too common

Individual Individual CharacteristicsCharacteristics

Properties of evidence that can be Properties of evidence that can be attributed to a common source with attributed to a common source with extremely high degree of certaintyextremely high degree of certainty

Examples:Examples:

1.1. Matching ridge characteristics of 2 Matching ridge characteristics of 2 fingerprintsfingerprints

2.2. Comparison of random striation markings Comparison of random striation markings on bullets or tool marks (figure 3-1)on bullets or tool marks (figure 3-1)

3.3. Comparison of irregular & random wear Comparison of irregular & random wear patterns in tire or footwear impressionspatterns in tire or footwear impressions


4.4. Handwriting Handwriting characteristicscharacteristics

5.5. Fitting together of Fitting together of irregular edges of irregular edges of broken pieces like broken pieces like a jigsaw puzzlea jigsaw puzzle

6.6. Matching Matching sequentially made sequentially made plastic bags by plastic bags by striation marks striation marks running across the running across the bags (figure3-2)bags (figure3-2)


Not possible to state with Not possible to state with mathematical exactness probability mathematical exactness probability that specimens are of common originthat specimens are of common origin

Conclusion must be made by Conclusion must be made by practical experience of the examinerpractical experience of the examiner probability of 2 individuals having probability of 2 individuals having

same fingerprints is 1 x 10same fingerprints is 1 x 106060


Individual characteristics can be used to Individual characteristics can be used to distinguish members of the same classdistinguish members of the same class

Forensic scientists try to individualize a Forensic scientists try to individualize a piece of physical evidence by some type of piece of physical evidence by some type of comparison processcomparison process

Only a few types of physical evidence Only a few types of physical evidence (primarily physical pattern evidence) can (primarily physical pattern evidence) can be truly individualizedbe truly individualized

The Ultimate GoalThe Ultimate Goal Ultimate goal would be to move all class Ultimate goal would be to move all class

evidence to individualistic which is not evidence to individualistic which is not very likelyvery likely

Hair is trying to make the Hair is trying to make the move...something like paint probably move...something like paint probably never will.never will.

For human evidence to be individualistic, For human evidence to be individualistic, the odds of two people matching the the odds of two people matching the same piece of evidence must be 1 in same piece of evidence must be 1 in about 7.5 billion, which is the population about 7.5 billion, which is the population of the earth. of the earth.

Class vs. IndividualClass vs. Individual When does evidence cross the line that When does evidence cross the line that

distinguishes class from individual distinguishes class from individual evidence?evidence? This is debated and disagreed among many This is debated and disagreed among many

forensic scientists.forensic scientists. How many striations are necessary to How many striations are necessary to

individualize a mark to a single tool and no individualize a mark to a single tool and no other?other?

How many color layers individualize a paint How many color layers individualize a paint chip to a single car?chip to a single car?

How many ridge characteristics individualize How many ridge characteristics individualize a fingerprint?a fingerprint?

Class vs. IndividualClass vs. Individual How many handwriting characteristics tie a How many handwriting characteristics tie a

person to a signature?person to a signature? Up to forensic scientist to find as many Up to forensic scientist to find as many

characteristics as possible to compare one characteristics as possible to compare one substance to another.substance to another.

Significant to consider:Significant to consider: QualityQuality Composition of evidenceComposition of evidence Case historyCase history Examiner’s experienceExaminer’s experience

Functions of the Forensic Functions of the Forensic ScientistScientist

A.A. Analysis of Physical Evidence Analysis of Physical Evidence

1. Apply scientific techniques to 1. Apply scientific techniques to analysis of evidence analysis of evidence

2. Be aware of demands and 2. Be aware of demands and constraints of legal systemconstraints of legal system

B. Provision of expert testimonyB. Provision of expert testimony

1. 1. Expert witness – an individual – an individual whom the court determines whom the court determines possesses knowledge relevant to the possesses knowledge relevant to the trial that is not expected of the trial that is not expected of the average personaverage person

2. Competency shown by degrees 2. Competency shown by degrees held, professional organizations held, professional organizations belong to, professional articles belong to, professional articles published, years of experience, published, years of experience, participation in special coursesparticipation in special courses


Expert WitnessExpert Witness

3. Opposing attorney may cross-3. Opposing attorney may cross-examine the witness & point out examine the witness & point out weaknesses in background or weaknesses in background or knowledgeknowledge

4. Laypersons testifying may not state 4. Laypersons testifying may not state their opinion, but an expert witness their opinion, but an expert witness cancan


C. Furnishing Training in the Proper C. Furnishing Training in the Proper Recognition, Collection, & Recognition, Collection, & Preservation of Physical EvidencePreservation of Physical Evidence

1. often have 1. often have Evidence Evidence TechniciansTechnicians on 24 hour call to aid on 24 hour call to aid criminal investigations in criminal investigations in retrieving evidenceretrieving evidence

2. where patrol officers or 2. where patrol officers or detectives gather the evidence, detectives gather the evidence, forensic scientist should train all forensic scientist should train all officers engaged in fieldworkofficers engaged in fieldwork