Transcript Finger Prints

Forensic Science:
An Introduction
Unit A: Crime Scene Processing
Definitions
Forensic Science - the application of the
knowledge and technology of science to
the criminal and civil laws that are
enforced by police agencies in a criminal
justice system.
 Locard’s Exchange Principle – when two
objects come in contact with each other, a
cross-transfer of materials occur. This
allows us to connect criminals to crime
scenes.
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The American Academy of Forensic
Science Departments
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Criminalistics - crime scene processing
Engineering Science - reconstruction
General
Jurisprudence - legal
Odontology - bitemarks
Pathology/Biology – autopsy, DNA
Physical Anthropology – skeletal remains
Psychiatry and Behavioral Science
Questioned Documents
Toxicology – drugs and poisons
Additional disciplines
Fingerprint examination
 Firearm and toolmark examination
 Computer and digital analysis
 Photography
 Entomology - insects
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Historical Events
Late 1700s - Arsenic and Toxicology
 Mid 1800s – Microscopy
 Late 1800s – Identification (Bertillion)
 Early 1900s – Fingerprinting, Blood and
Serology, Document Examination,
Microscopy
 Mid 1900s – Chromatography,
Spectrophotometry, Electrophoresis, DNA
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Publications
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Yi Yu Ji “A Collection of Criminal Cases”
“A Treatise on Forensic Medicine and Public
Health” (Fodere, 1798)
“Finger Prints” (Galton, 1892)
“Criminal Investigation” (Gross, 1893)
Sherlock Holmes –fiction (Doyle 1880s)
“Treaty of Criminalistics (Locard, 1931)
Hypervariable Minisatellite Regions in Human
DNA (Jeffreys, 1985)
Crime Labs
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Locard
Los Angeles - oldest
FBI
DEA
ATF
US Postal Service
SBI
State system
Local
Delocalized labs – no common management
Crime Lab Services
Basic Services
 Photography
 Physical Science
 Biology/DNA
 Firearms
 Document
Examination
Optional Services
 Toxicology
 Latent Fingerprint
 Polygraphy
 Voice Analysis
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Forensic Psychiatry
Forensic Odontology
Forensic Engineering
Forensic Computer
and Digital Analysis
What Forensic Scientists Do
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Analyze physical evidence
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Determine admissibility of evidence
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Use scientific methods
Frye v US (1923) – general acceptance
Judge scientific evidence
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Daubert case (1993) – trial judge is gatekeeper
Provide expert testimony
 Furnish training
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Forensic Science
Forensic scientist seek to reach truth
based on available evidence. The legal
process does not, however, always seek
truth but follow process.
 Reliable methods possess characteristics
of:
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Integrity
 Competence
 Defensible technique
 Relevant experience
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Reliable Methods
Help distinguish evidence from
coincidence
 Allow alternative results to be ranked by
basic scientific principles
 Allow tests to either prove or disprove
alternative hypotheses
 Pursue testing by breaking hypotheses
into their smallest logical components
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Physical Evidence
Anything physical objects that can link a
crime to its victims or to suspects.
 Has to be collected from crime scene
 Must be relevant to the crime
 Requires the collector to understand what
the capabilities and limitations of the crime
lab are
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Physical Evidence
Crime labs do not solve crimes, only add
evidence to help police investigation link
the suspect to the crime.
 The forensic scientists must know how to
collect and preserve evidence found at the
crime scene
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Ways to classify a crime scene
Primary vs secondary crime scene
 Macroscopic vs microscopic scenes
 Type of crime
 Location of crime
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Use of Physical Evidence
Information on evidence of a crime
(Corpus Delecti)
 Information on the criminal (Modus
Operandi)
 Linkage on persons, scenes and objects
 Identification of suspects
 Identification of unknown substances
 Reconstruction of a crime
 Providing investigative leads
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Arriving at the Crime Scene
Secure and isolate the crime scene
 Determine boundaries of crime scene and
priorities for evidence collection
 Rough sketch
 Finished sketch
 Photograph
 Videotaping
 Notes
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Collecting Evidence
Conduct a systematic search for evidence;
be unabiased and thorough.
 Field technicians
 What to look for depends on the crime and
what specific locations of the crime scene
would most likely be affected
 Microscopic or massive objects
 Collect carriers of possible evidence
 Vacuum or sweeping collected
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Packaging of Evidence
Prevent any changes from occurring
(contamination, breakage, evaporation,
bending, loss)
 Process trace evidence from original
object (shirt, shoe) rather than isolating
and packaging if possible
 Package evidence separately
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Tools for Collecting Evidence
Forceps
 Evidence envelopes and pill bottles
 Swabs
 Special concerns (mold, evaporation)
 Various light sources
 Latent fingerprints
 Mobile crime labs or better yet crime
scene search vehicle
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Chain of custody
Continuity of possession; every person
who touched it must be accounted for
 Standards for collecting, labeling, and
submitting evidence forms are necessary
for court
 Labels include collectors initials, location
of evidence, date of collection.
Identification numbers must also be used
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Submission of Evidence
Standard/reference samples
 Substance controls
 Evidence submission form will detail the
evidence collect and particular type of
examination/analysis requested.
 Lab tech not bound by requests
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Common Types of Evidence
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Common Types of
Evidence
Blood, semen, and saliva
Documents
Drugs
Fibers
Fingerprints
Firearms and ammunition
Glass
Hair
Impressions
Organs and physiological
fluids
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Paint
Petroleum products
Plastic bags
Plastic, rubber, and other
polymers
Powder residues
Serial numbers
Soil and minerals
Tool marks
Vehicle lights
Wood and other
vegetative matter
Examination of Physical Evidence
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Identification
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Determining the identity of a substance with a near
absolute certainty while ruling out other substances
Comparison
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Comparing the evidence to one or more selected
references and drawing a conclusion about its origins.
Individual characteristics –properties of evidence that
can be attributed to a common source with extremely
high certainty. (eg. fingerprints, DNA, bullets)
Class characteristics – properties of evidence that
can be associated with a group and never with a
single source. ( eg. Blood type, tire marks)
Significance of Physical Evidence
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Assessing the values of evidence
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Class characteristics of evidence is valuable in
corroborating events.
Multiple class evidence can lead to a high level of
certainty of origin
Cautions and limitations of evidence
A person can be exonerated or excluded from
suspicion if evidence collected from the crime
scene is different from the reference samples
collected from the person.
Forensic Databases
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One-on-one comparison requires a suspect
Computerized databases help link evidence to
people
Fingerprint databases – IAFIS
DNA database – CoDIS
Ballistics database – IBIS
Automative Paint database – PDQ
Shoeprint database - SICaR
Crime-Scene Reconstruction
The method used to support a likely
sequence of events at a crime scene by
observing and evaluating physical
evidence and statements made by those
involved with the incident
 Combined efforts of MEs, CSI, and law
enforcement personnel
 Examples: was body moved, bullet
trajectory, blood splatter
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History
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Alphonse Bertillion (1883) – anthropometry
Henry Fauld (1880) - first published on possible
use of fingerprints
Francis Galton (1892) – published Finger Prints
described types of prints
Sir Edward Henry (1897) – classification system
used today
FBI (1924) – new formed FBI held world’s
largest fingerprint database
Fingerprint Principles
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1. A fingerprint is an individual characteristic; no two
fingerprints have been found to possess identical ridge
characteristics
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2. A fingerprint remains unchanged during an individual’s
lifetime
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No minimum number of comparisons to establish identity
Friction ridges and grooves created by dermal papillae
Sweat glands on the ridges deposit perspiration and oils
Latent fingerprint – left by deposits and is invisible to the naked
eye
3. Fingerprints have general ridge patterns that permit
them to be systematically classified.
Categories of Fingerprints
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Loop – ridge lines enter one side of
pattern and curve around to exit from the
same side of pattern. (65%)
Ulnar loop – opens toward little finger
 Radial loop – opens toward thumb
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Ulnar Loop
Radial Loop
Categories of Fingerprints
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Whorl – ridge lines rounded or circular and
have two deltas(30-35%)
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Plain whorl
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Central pocket loop
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Double loop
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Accidental loop
Categories of Fingerprints
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Arch – ridge lines enter print from one side
and exit from the other (5%)
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Plain
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Tented
Classification of Fingerprints
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Henry system – numerical system involving the
presence or absence of the whorl pattern on
each finger as part of the primary classification..
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This does not identify someone, only reduce the
number of possible candidates
AFIS – 10 print system that can search 500,000
stored ten-prints in 0.8 seconds
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Data entered now by Livescan rather than ink rolling.
Human decisions must still be made
Software incompatibilities among states
Methods of Detection
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Types of prints
Latent print
 Visible print – deposited ink, blood, dirt
 Plastic print – impression in a soft surface
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Locating prints – RUVIS
Developing Prints
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Powders
Charcoal
 Magnetic
 Fluorescent
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Chemicals
Iodine fuming (sublimation)
 Ninhydrin
 Physical developer (silver nitrate)
 Super Glue fuming
 Alternate Light Sources/ LED
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Preservation of Developed
Prints
Photographs
 Print surface should be removed in its
entirety (covered with cellophane)
 Lifted from surface with tape
 Digital imaging into pixels – allows
adjustments to be made to enhance
picture
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