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Introduction to Forensic Science

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Title: Introduction to Forensic Science


1
Introduction to Forensic Science
  • A Short Guide for the Perplexed

2
The CSI Effect
3
The CSI Effect
4
The CSI Effect
  • Juries expect the kind of forensic science shown
    on CSI
  • Unfortunately, 40 of the forensic science shown
    on CSI does not exist

5
Before CSI
6
Before CSI
7
Before CSI
8
Before CSI
9
What is Forensic Science?
  • Forensic science is the application of scientific
    principles to the resolution of legal issues in
    criminal, civil and administrative hearings

10
Forensic Science Specialties
  • Criminalistics
  • Firearms and tool mark examination
  • Document examination
  • Fingerprint identification
  • Forensic photography and image analysis
  • Computer forensics

11
Forensic Science Specialties
  • Forensic pathology
  • Forensic odontology (forensic dentistry)
  • Forensic anthropology
  • Forensic toxicology
  • Forensic psychiatry
  • Forensic psychology (includes criminal profiling)

12
Criminalistics
  • Drug chemistry
  • Trace evidence analysis
  • Hairs and fibers
  • Glass and soil
  • Paint and plastics
  • Ignitable liquids (arson accelerants)
  • Explosive residues
  • Gunshot residues
  • Forensic biology
  • Forensic molecular biology (i.e. DNA profiling)

13
Types of Evidence
  • Testimonial
  • Documentary
  • Demonstrative
  • Physical

14
Uses of Physical Evidence
  • To prove elements of the crime
  • To identify the perpetrator
  • To reconstruct the crime
  • To confirm or refute the statements of
  • Complainants
  • Witnesses
  • Suspects

15
Types of Physical Evidence
  • Pattern evidence
  • Trace evidence

16
Pattern Evidence
  • Fingerprints
  • Foot impressions
  • Footwear impressions
  • Tire impressions
  • Striation patterns on bullets, breechblock
    markings, tool marks
  • Powder and shotgun pellet patterns
  • Char and soot patterns
  • Handwriting/typewriting
  • Bloodstain (and other body fluid) patterns

17
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18
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19
What is Trace Evidence?
  • Trace evidence refers to the minute bits of
    physical evidence that may be exchanged among the
    perpetrator of a crime, the victim and the crime
    scene

20
The Locard Exchange Principle
  • The Locard Exchange Principle states that when
    two surfaces come into contact, an exchange of
    trace evidence takes place across the interface
    between them
  • Every touch leaves a trace.

21
Types of Trace Evidence
  • Solid aggregates
  • Fibrous (hairs, fibers, botanical samples)
  • Particulate (glass, soil, metal fragments, paint
    chips and smears, explosive residues, gunshot
    residues)
  • Liquids
  • Blood, semen and other body fluids
  • Molecular traces
  • Explosive residues, ignitable liquid residues

22
Forensic Analysis of Particulate Trace Evidence
  • Microscopic examination
  • Instrumental methods of analysis as appropriate

23
Infrared Microscopy Combined with
Fourier-Transform Infrared Spectrometry
24
Infrared Spectra of Artificial Hair StrandsThe
Jeffrey McDonald Case
25
Forensic Biology and Forensic Molecular Biology
26
Body Fluids Examined in the Forensic Science
Laboratory
  • Blood
  • Semen
  • Saliva
  • Urine
  • Feces
  • Perspiration

27
Screening Suspected Bloodstains
  • Is that red-brown stain a bloodstain?
  • If it isnt blood we dont want to include it in
    our blood spatter analysis
  • If it isnt blood we dont want the forensic
    biologist to waste time processing it as blood
    evidence

28
Forensic Analysis of Suspected Bloodstains
  • Presumptive tests
  • Confirmatory tests
  • Species identification tests
  • DNA profiling

29
Composition of Blood
  • Cellular components
  • Erythrocytes (red blood cells)
  • Leukocytes (white blood cells)
  • Platelets
  • Fluid
  • Water
  • Dissolved salts
  • Proteins
  • Human serum albumin
  • Globulins (alpha-, beta- and gamma-globulin)

30
Human Erythrocytes
31
Commercial Blood Test Kits
32
Luminol
33
Luminol
34
Confirmatory Tests for Blood
  • Takayama test
  • A crystal test for hemoglobin
  • Pink, leaf-like birefringent crystals are formed
  • Microspectroscopy
  • Identifies the characteristic absorption spectrum
    of hemoglobin

35
Takayama Crystals
36
Takayama Crystals
37
Human Blood Identification
Hexagon OBTI
  • Test kits are available for the identification of
    human blood at crime scenes
  • These are based on the reaction of human
    hemoglobin with anti-human hemoglobin antibodies

38
The Death of Dale Earnhart
39
DNA Profiling
40
Structure of DNA
  • DNA (deoxyribonucleic acid) is composed of three
    components
  • Phosphate groups
  • Sugars (deoxyribose)
  • Bases
  • Adenine (A)
  • Thymine (T)
  • Guanine (G)
  • Cytosine (C)

41
Double-Stranded (Duplex) DNA
42
Mutations
  • The genetic information in DNA can be changed by
    mutations
  • Point mutations (one base substitutes for
    another)
  • Insertions
  • Deletions
  • Natural selection constrains the variability of
    functional DNA (i.e. genes)
  • Non-functional DNA has greater variability

43
DNA Extraction
  • Remove cellular material (cell membranes,
    proteins etc.)
  • Dissociate nuclear DNA from histones
  • Purify DNA

44
Types of Samples
  • Body fluids
  • Blood
  • Tissues
  • Muscle
  • Bone
  • Teeth
  • Body fluid stains
  • Bloodstains
  • Semen stains
  • Saliva stains
  • Urine stains

45
PCR The Molecular Xerox Machine
  • Polymerase chain reaction (PCR) is used to make
    copies of DNA strands
  • To aid judges and juries in understanding what
    PCR does many experts compare PCR to using a
    Xerox copier to make very many copies of the page
    of a book.
  • A more accurate analogy is using a Xerox copier
    to make many copies of a sentence on a page in a
    book.

46
The CODIS System
  • CODIS Combined DNA Index System
  • CODIS began as a pilot project in 1990 serving 14
    state and local laboratories.
  • The DNA Identification Act of 1994 (Public Law
    103 322) formalized the FBI's authority to
    establish a national DNA index for law
    enforcement purposes.
  • In October 1998 the FBI's National DNA Index
    System (NDIS) became operational.
  • CODIS is divided into two indices the forensic
    index and the offender index

47
The CODIS Core Loci
  • The FBI has identified 13 short-tandem repeat
    (STR) loci as core loci for the CODIS system
  • If a known sample of DNA matches the questioned
    sample at all 13 loci the DNA expert can state
    that both DNA samples came from the same source

48
ABI PRISM 310 Genetic Analyzer
49
Nuclear DNA STR data
50
DNA DatabasesCases Aided by CODIS
51
DNA Databases
  • CODIS (Combined DNA Index System)
  • NDIS (National DNA Index System) has 4,398,639
    DNA profiles
  • Total Forensic profiles¬† 167,103
  • Total Convicted Offender profiles¬† 4,231,536
  • The UKs ten locus STR database uses eight of the
    thirteen loci used in the CODIS database

52
DNA Sequencing
  • The actual sequence of As, Ts, Gs and Cs is the
    ultimate genetic information
  • The Human Genome Project has sequenced the entire
    human genome

53
Mitochondrial DNA Sequencing
  • Mitochondria contain loops of DNA
  • Each mitochondrion contains several loops of DNA
  • Each cell contains a number of mitochondria
  • Mitochondrial DNA (mtDNA) is maternally inherited

54
Mitochondrial DNA Sequencing
55
Mitochondrial DNA Sequencing
  • In human mtDNA the D-loop (or control region)
    contains two hypervariable regions (HV-1 and
    HV-2)
  • The hypervariable regions can be sequenced using
    appropriate primers

56
Mitochondrial DNA sequence data
57
Advantages and Disadvantages of MtDNA Sequencing
  • There are more copies of mtDNA than nuclear DNA
  • MtDNA can be recovered and sequenced from
    difficult samples
  • Degraded samples
  • Samples lacking significant intact DNA (hair)
  • Due to size of mtDNA database frequency estimates
    are not possible

58
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59
DNA Profiling and the War on Terror
  • Identification of victims (e.g. World Trade
    Center)
  • DNA profiles from improvised explosive devices
    (IEDs)
  • Microbial forensic database

60
My Background
  • Education
  • BS in Chemistry (Emory University)
  • AM (1968), PhD (1976) in Chemistry (Harvard
    University)
  • Forensic Science Experience
  • 1969-1971 Forensic chemistry specialist, US Army
    Criminal Investigation Laboratories (drug
    chemistry and forensic serology)
  • US Army CID investigator

61
Major Cases
  • The Jeffrey McDonald Case
  • The death of Dale Earnhart
  • The exhumation of Jesse James

62
Forensic Science at The George Washington
University
  • We offer the Master of Forensic Science degree
  • Students may specialize in
  • Crime Scene Investigation
  • Forensic Chemistry
  • Forensic Molecular Biology
  • Forensic Toxicology
  • High Technology Crime Investigation
  • Security Management
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