Introduction to Forensic Science

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Introduction to Forensic Science

• A Short Guide for the Perplexed

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The CSI Effect
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The CSI Effect
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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

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Before CSI
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Before CSI
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Before CSI
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Before CSI
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What is Forensic Science?

• Forensic science is the application of scientific
  principles to the resolution of legal issues in
  criminal, civil and administrative hearings

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Forensic Science Specialties

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

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Forensic Science Specialties

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

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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)

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Types of Evidence

• Testimonial
• Documentary
• Demonstrative
• Physical

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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

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Types of Physical Evidence

• Pattern evidence
• Trace evidence

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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

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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

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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.

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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

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Forensic Analysis of Particulate Trace Evidence

• Microscopic examination
• Instrumental methods of analysis as appropriate

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Infrared Microscopy Combined with
Fourier-Transform Infrared Spectrometry
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Infrared Spectra of Artificial Hair StrandsThe
Jeffrey McDonald Case
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Forensic Biology and Forensic Molecular Biology
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Body Fluids Examined in the Forensic Science
Laboratory

• Blood
• Semen
• Saliva
• Urine
• Feces
• Perspiration

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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

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Forensic Analysis of Suspected Bloodstains

• Presumptive tests
• Confirmatory tests
• Species identification tests
• DNA profiling

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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)

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Human Erythrocytes
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Commercial Blood Test Kits
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Luminol
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Luminol
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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

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Takayama Crystals
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Takayama Crystals
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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

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The Death of Dale Earnhart
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DNA Profiling
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Structure of DNA

• DNA (deoxyribonucleic acid) is composed of three
  components
• Phosphate groups
• Sugars (deoxyribose)
• Bases
• Adenine (A)
• Thymine (T)
• Guanine (G)
• Cytosine (C)

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Double-Stranded (Duplex) DNA
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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

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DNA Extraction

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

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Types of Samples

• Body fluids
• Blood
• Tissues
• Muscle
• Bone
• Teeth
• Body fluid stains
• Bloodstains
• Semen stains
• Saliva stains
• Urine stains

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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.

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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

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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

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ABI PRISM 310 Genetic Analyzer
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Nuclear DNA STR data
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DNA DatabasesCases Aided by CODIS
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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

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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

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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

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Mitochondrial DNA Sequencing
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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

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Mitochondrial DNA sequence data
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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

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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

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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

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Major Cases

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

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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