Introduction to Forensic Science and Crime Scene Processing

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Introduction to Forensic Science and Crime Scene
Processing

• Glenn Langenburg
• Forensic Scientist/Latent Print Examiner
• MN Bureau of Criminal Apprehension

Lecture 1
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Outline

• Forensic Science
• Chemistry
• Biology
• Identification
• Basics of Evidence
• Value of Physical Evidence

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Forensic Science Disciplines

• Chemistry (Physical sciences)
• Drugs
• Trace Evidence
• Toxicology
• Biology
• DNA
• Serology
• Identification (Criminalistics)
• Fingerprints
• Firearms/Toolmarks
• Footwear/Tire Tracks
• Questioned Documents

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Drug Chemistry

• Drug
• A natural or synthetic substance that is used to
  produce physiological or psychological effects in
  humans or animals
• Controlled substance
• The sale and distribution is tightly controlled
• Controlled Substances Act (Sched. I-V)

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Trace Evidence

• Soil analysis
• Paint analysis
• Fiber analysis
• Glass analysis

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Forensic Toxicology

• Study of poisons
• Drugs in blood and urine
• Blood and breath alcohol

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Forensic Biology

• Forensic Serology
• Forensic Characterization of Semen
• DNA

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Criminalistics

• Latent Prints
• Toolmarks
• Firearms
• Footwear Impressions
• Tire Tracks
• Questioned Documents

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Basic Principles

• Forensic Science
• it is the application of science to those
  criminal and civil laws that are enforced by
  police agencies in a criminal justice system
• Physical Evidence
• any object that can establish that a crime has
  been committed or can provide a link between a
  crime and its victim or between a crime and its
  perpetrator

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Types of Evidence

• Physical evidence
• Eyewitness testimony
• Evidence
• Probative and reliable
• Incriminating
• Exculpatory

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Physical Evidence

• Class characteristics
• Evidence can only be associated with a group and
  not a unique source
• Individual characteristics
• Evidence can be attributed to a unique source
  with a high degree of certainty (or even to the
  exclusion of all others)

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Examples of Class Characteristics

• Shoes (Nike, Air Jordan, size 9)
• Paint (Cherry red 1967 Chevy Mustang)
• Fibers (Red polyester fiber, braided weave)
• Fingerprints (loops, whorls, arches)
• Toolmarks (1/4 flat blade BD screwdriver)
• Firearms (.40 caliber SW magnum pistol)
• Arson (accelerants)
• DNA (male)

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Examples of Unique Characteristics

• Shoes (natural wear, bubble gum)
• Paint (physical match)
• Fibers (physical match, unique trait)
• Fingerprints (ridge detail)
• Toolmarks (stria markings)
• Firearms (stria, firing pin markings)
• DNA (profile)

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Scenarios

• Pathology wound matches murder weapon
• Glass fragments found in burglars coat pocket
• Burglars tools
• Poison found in suspects home with rare
  component

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Analysis of Evidence

• Known
• Unknown
• Common Source
• e.g. the unknown XXX collected at the crime scene
  was compared to known XXX collected from Ms. Y
  and could have originated from a common source.

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Analysis of Evidence

• Known
• Unknown
• Common Source
• e.g. the unknown XXX collected at the crime scene
  was compared to known XXX collected from Mr. Y
  and found to have a common source.

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Scenarios

• Blood stains found at the crime scene were
  collected and compared against a DNA profile
  obtained from the blood collected from Jim Jones.

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Scenarios

• Blood stains found at the crime scene were
  collected and compared against a DNA profile
  obtained from the blood collected from the victim
  Sharon Jones.

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Scenarios

• Blood stains found at the crime scene were
  collected and compared against a DNA profile
  obtained from the blood collected from the
  unidentified deceased female.

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Scenarios

• Blood stains found on the suspects clothing were
  compared against a DNA profile obtained from the
  victim Sharon Jones.

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Scenarios

• Blood collected from suspect was compared against
  a DNA profile blood obtained from small stains on
  the suspects clothing.

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Scenarios

• Paint chips collected at the scene of a hit and
  run were compared against paint scrapings from
  the suspects vehicle.
• Red paint smears collected from suspects vehicle
  were compared against paint samples from the
  victims bicycle.

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Scenarios

• A DNA profile from the unidentified baby was
  compared against a DNA profile obtained from Mr.
  Jacobs.
• Fingerprints obtained from Mr. Jacobs were
  compared against a fingerprint card from a
  previous arrest of Mr. Jacobs.
• Latent fingerprints found at the scene of a
  murder in Atlanta, GA were compared against
  fingerprints found at the scene of a murder in
  Albany, NY.

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Analysis of Evidence

• Control
• control expect positive reaction
• - control expect no reaction
• False Reactions
• False positive , but not true
• False negative -, but not true

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Analysis of Evidence

• Limited sample
• Trade-offs
• Use least consuming techniques
• Least to most destructive techniques

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Edmond Locard (1877-1966)

• French investigator
• Background in medicine and law
• 1910-started a police laboratory
• Founded Institute of Criminalistics at the
  University of Lyons
• Contributed to fingerprints (poroscopy)

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Locards Exchange Principle

• Principle of cross-transfer
• Whenever two objects come into contact there is
  evidence of that contact through cross-transfer
• Microscopic
• Macroscopic

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Physical Evidence Can

• 1. Prove that a crime has been committed or
  establish key elements of a crime
• Example
• Rape victim has torn clothing, bruises, broken
  arm non-consensual

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Physical Evidence Can

• 2. Link a suspect with the victim or crime scene
• Example
• Burglary suspect has broken glass shards in his
  pants cuff that are consistent with glass shards
  at scene

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Physical Evidence Can

• 3. Establish the identity of persons associated
  with a crime
• Example
• Latent fingerprints identified through AFIS. DNA
  identified through CODIS.

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Physical Evidence Can

• 4. Exonerate the innocent
• Example
• Rape DNA preserved was compared against man
  convicted of the crime no match.

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Physical Evidence Can

• 5. Corroborate the victims story
• Example
• Officer involved shootings

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Physical Evidence Can

• 6. Contradict information provided to
  investigators
• Example
• Discredit a witness elicit a confession

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Physical Evidence Can

• 7. Be more reliable than eyewitness testimony
• Physical Evidence does not forget. It is not
  confused by the excitement of the moment. It is
  not absent because human witnesses are. It is
  factual evidence. It cannot be wrong it cannot
  perjure itself it cannot be wholly absent. Only
  in its interpretation can there be error. Only
  human failure to find, study, and understand it
  can diminish its value.
• Paul Kirk, Crime Investigation, 1953

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Physical Evidence Can

• 8. Be the cornerstone of a case
• Police/prosecutors are expected to obtain
  physical evidence and rarely rely on a confession
  alone

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Physical Evidence Can

• 9. Expected by a jury/the public
• TV, books, media focus on physical evidence and
  the miracles performed (reality vs. fantasy)

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Lack of Physical Evidence Can

• 10. Support or refute a theory
• The absence of forced entry in a burglary case