Transcript Physical Evidence

Physical Evidence
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Objectives
List the common types of physical evidence encountered at crime scenes.
Explain the difference between the identification and comparison of physical evidence.
Define individual and class characteristics. Give examples of physical evidence
possessing these characteristics.
Discuss the value of class evidence to a criminal investigation.
List the number and types of computerized databases relating to physical evidence
that are currently in existence.
Explain the purpose physical evidence plays in reconstructing the events surrounding
the commission of a crime.
Updated 7/17/2015
Created by C. Ippolito July 2007
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Common Types of Physical Evidence
• Blood, Semen, and Saliva
• on fabrics
• cigarette butts
• Documents
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handwriting
typewriting
paper, ink, obliterations
charred/burned documents
• Drugs
• any illegal substances
Updated 7/17/2015
Created by C. Ippolito July 2007
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Common Types of Physical Evidence
• Explosives
• devices
• objects from scene
• Fibers
• natural
• synthetic
• Fingerprints
• hidden
• visible
Updated 7/17/2015
Created by C. Ippolito July 2007
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Common Types of Physical Evidence
• Firearms
• discharged ammo
• intact ammo
• Glass
• particles/fragments
• bullet holes in panes
• Hair
• animal
• human
Updated 7/17/2015
Created by C. Ippolito July 2007
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Common Types of Physical Evidence
• Impressions
• tires
• shoes
• bite marks
• Organs/Physiological Fluids
• evidence of drugs/poison
• alcohol levels
• Paint
• liquid/dry/chips
• cross transfers
Updated 7/17/2015
Created by C. Ippolito July 2007
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Common Types of Physical Evidence
• Petroleum Products
• arson accelerants
• grease stains
• Plastics
• bags used in crimes
• cross transfer
• Powder Residue
• GSR
• Serial Number
• restore ID firearms etc
Updated 7/17/2015
Created by C. Ippolito July 2007
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Common Types of Physical Evidence
• Soil/Minerals
• imbedded in shoes
• insulation on garments
• Tool Marks
• impressions
• Vehicle Lights
• Wood/Vegetative Matter
• wood, sawdust, pollen
Updated 7/17/2015
Created by C. Ippolito July 2007
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Examination of Physical Evidence
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Identification
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determine the physical or chemical identity of a substance
1. adopt test procedure with characteristic results for standard
materials
2. test sufficient to exclude other substances
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Comparison
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subjects suspect specimen and a standard specimen to
same tests to determine common origin
1. select properties are chosen for comparison
2. draw conclusion about origin
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Probability of likelihood of similar origin is important
Updated 7/17/2015
Created by C. Ippolito July 2007
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Individual Characteristics
• property possessed by evidence that can be
associated with a common source with an
extremely high degree of probability
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matching fingerprint ridge marks (1 x 1060)
comparison of random striations on bullets or tools
comparison of wear patterns in footwear or tires
comparison of handwriting characteristics
Updated 7/17/2015
Created by C. Ippolito July 2007
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Class Characteristics
• evidence that can be associated with a group of
specimens but cannot be singled out as coming
from a single source
• single layer paint chip from a car
• blood types (26% of population has type A)
• need additional characteristics to “increase” probability of
difference
• product rule
• overall probability of multiple characteristics existing together
is the product of their individual probabilities
• Type A – 26%, EsD factor - 85%, PGM 2+2- - 2%
• total probabilit together .26 x .85 x .02 = .0044 or 1/200
Updated 7/17/2015
Created by C. Ippolito July 2007
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Significance of Physical Evidence
• Forensic Science cannot for the most part assign
exact or approximate probability values in the
comparison of the vast majority of class physical
evidence
• create databases of statistical significance
• Value of Class Physical Evidence
• does it corroborate events?
• variety of evidence convicted W. Williams in Georgia murders
• can more often can exonerate or exclude individuals
• When does evidence cross from “class” to “individual”
• how many ridges in a fingerprint?
• how many writing similarities?
Updated 7/17/2015
Created by C. Ippolito July 2007
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Natural vs Evidential Variation
• Modern analysis can find differences in the
same material
• Criminalists must distinguish natural variation from
evidential variation
• at one magnification paint chips indistinguishable
• at greater magnification difference can be discerned
• when are the differences and similarities
significant?
Updated 7/17/2015
Created by C. Ippolito July 2007
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Forensic Databases
• Integrated Automated Fingerprint Identification System (IAFIS)
• FBI maintained
• fingerprints and criminal histories of 50 million individuals
• scanned latent can be compared by computer and list of possible matches will be
returned
• similar systems in other countries
• Combined DNA Index System (CODIS)
• FBI maintained
• DNA profiles
• Forensic Index – 110,000 profiles of unknowns from unsolved crimes
• Offender Index – 3 million profiles of convicted/arrested individuals
• National Integrated Ballistics Information Network (NIBIN)
• Bureau of Alcohol Tobacco Firearms and Explosives maintained
• ballistic images stored and correlated submitted by local jurisdictions
• International Forensic Automotive Paint Data Query (PDQ)
• RCMP maintained
• chemical and color information on original automotive paints
• Shoeprint Image Capture and Retrieval (SICAR)
• commercially maintained database for shoe sole patterns (8,000) form 300 shoe
manufacturers
Updated 7/17/2015
Created by C. Ippolito July 2007
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Crime Scene Reconstruction
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examining evidence to reconstruct the events
that occurred before, during, and after the
commission of a crime
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evidence supports a likely sequence of events
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collaboration and collect /analysis of data by:
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Updated 7/17/2015
medical examiners
criminalists
law enforcement
Created by C. Ippolito July 2007
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