Chapter 3Chapter 3

Physical EvidencePhysical Evidence

Common Types of Physical Common Types of Physical EvidenceEvidence

Blood, semen & salivaBlood, semen & saliva DocumentsDocuments DrugsDrugs ExplosivesExplosives FibersFibers FingerprintsFingerprints Firearms & ammunitionFirearms & ammunition GlassGlass

Physical Evidence from A-ZPhysical Evidence from A-Z

HairHair ImpressionsImpressions Organs and physiological fluidsOrgans and physiological fluids PaintPaint Petroleum productsPetroleum products Plastic bagsPlastic bags Plastic, rubber, and other polymersPlastic, rubber, and other polymers Powder residuesPowder residues Serial numbersSerial numbers Soil and mineralsSoil and minerals Tool marksTool marks Vehicle lightsVehicle lights Wood and other vegetative matterWood and other vegetative matter

Identification vs. Identification vs. ComparisonComparison

IdentificationIdentification the process of determining the the process of determining the

physical or chemical identity of a physical or chemical identity of a substancesubstance

What are some examples?What are some examples?

Examples of Physical Evidence Examples of Physical Evidence to be identifiedto be identified

Drugs, species determination, Drugs, species determination, explosive residueexplosive residue

Drug AnalysisDrug Analysis

Australian Federal Police via Getty

ImagesForensic technicians are often called to identify unknown drugs. A beauty student allegedly tried to smuggle more than 10,000 amphetamine tablets into Australia.

ComparisonComparison

Determining whether 2 or more Determining whether 2 or more objects have a common originobjects have a common origin

What is required?What is required? A standard/reference sampleA standard/reference sample Results may be reported as Results may be reported as

probability (frequency of occurrence probability (frequency of occurrence of an event)of an event)

Individual CharacteristicsIndividual Characteristics

Properties of evidence that can be Properties of evidence that can be attributed to a common source with attributed to a common source with an extremely high degree of an extremely high degree of certaintycertainty

Victor Balthazard probability of 2 Victor Balthazard probability of 2 identical identical

fingerprints is one in 1X 10fingerprints is one in 1X 106060

See Examples on p. 66 See Examples on p. 66 CriminalisticsCriminalistics

Class CharacteristicsClass Characteristics

Properties of evidence that can only Properties of evidence that can only be associated with a group and never be associated with a group and never with a single sourcewith a single source

http://science.howstuffworks.com/forensic-lab-http://science.howstuffworks.com/forensic-lab-technique.htm/printabletechnique.htm/printable

(Video Forensic analysis of a gun)(Video Forensic analysis of a gun) http://videos.howstuffworks.com/science/fingerprint-videos-http://videos.howstuffworks.com/science/fingerprint-videos-

playlist.htm#video-3949playlist.htm#video-3949 The Black Hand Mob in NYC circa 1903The Black Hand Mob in NYC circa 1903

Examples of Class Examples of Class CharacteristicsCharacteristics

Paint samples from a hit-and-runPaint samples from a hit-and-run Multiple layered samples increase Multiple layered samples increase

the probability of “matching” a the probability of “matching” a known sampleknown sample

http://www.kcra.com/r/24405935/detail.htmlhttp://www.kcra.com/r/24405935/detail.html

Examples of Class Examples of Class CharacteristicsCharacteristics

BloodBlood Blood type alone may not be a basis Blood type alone may not be a basis

to establish common originto establish common origin Product Rule- multiplying together Product Rule- multiplying together

the frequencies of independently the frequencies of independently occurring genetic markers to obtain occurring genetic markers to obtain an overall frequency of occurrence an overall frequency of occurrence for a genetic profile (see p. 67)for a genetic profile (see p. 67)

Who decides?Who decides?

The weight or significance of physical The weight or significance of physical evidence in a case is usually left to evidence in a case is usually left to the jury. the jury.