Forensic Science: An Introduction

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Forensic Science An Introduction

• Unit A Crime Scene Processing

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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.
• Locards 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

• 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

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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

• 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)

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Crime Labs

• Locard
• Los Angeles - oldest
• FBI
• DEA
• ATF
• US Postal Service
• SBI
• State system
• Local
• Delocalized labs no common management

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Crime Lab Services

• Basic Services
• Photography
• Physical Science
• Biology/DNA
• Firearms
• Document Examination

• Optional Services
• Toxicology
• Latent Fingerprint
• Polygraphy
• Voice Analysis
• Forensic Psychiatry
• Forensic Odontology
• Forensic Engineering
• Forensic Computer and Digital Analysis

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What Forensic Scientists Do

• Analyze physical evidence
• Use scientific methods
• Determine admissibility of evidence
• Frye v US (1923) general acceptance
• Judge scientific evidence
• 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
• 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/analysi
  s requested.
• Lab tech not bound by requests

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Common Types of Evidence

• Common Types of Evidence
• Blood, semen, and saliva
• Documents
• Drugs
• Fibers
• Fingerprints
• Firearms and ammunition
• Glass
• Hair
• Impressions
• Organs and physiological fluids

• 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

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Examination of Physical Evidence

• Identification
• Determining the identity of a substance with a
  near absolute certainty while ruling out other
  substances
• Comparison
• 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)

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Significance of Physical Evidence

• Assessing the values of evidence
• 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.

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Forensic Databases

• 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

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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

• 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 worlds largest
  fingerprint database

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Fingerprint Principles

• 1. A fingerprint is an individual characteristic
  no two fingerprints have been found to possess
  identical ridge characteristics
• No minimum number of comparisons to establish
  identity
• 2. A fingerprint remains unchanged during an
  individuals lifetime
• 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.

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Categories of Fingerprints

• 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

Ulnar Loop
Radial Loop
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Categories of Fingerprints

• Whorl ridge lines rounded or circular and have
  two deltas(30-35)
• Plain whorl
• Central pocket loop
• Double loop
• Accidental loop

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Categories of Fingerprints

• Arch ridge lines enter print from one side and
  exit from the other (5)
• Plain
• Tented

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Classification of Fingerprints

• Henry system numerical system involving the
  presence or absence of the whorl pattern on each
  finger as part of the primary classification..
• 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
• Data entered now by Livescan rather than ink
  rolling.
• Human decisions must still be made
• Software incompatibilities among states

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Methods of Detection

• Types of prints
• Latent print
• Visible print deposited ink, blood, dirt
• Plastic print impression in a soft surface
• Locating prints RUVIS

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Developing Prints

• Powders
• Charcoal
• Magnetic
• Fluorescent
• 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