Download Introduction to Forensic Science

Introduction to Forensic Science
A Short Guide for the Perplexed
The CSI Effect
The CSI Effect
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
Before CSI
Before CSI
Before CSI
Before CSI
What is Forensic Science?
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Forensic science is the application of
scientific principles to the resolution of
legal issues – in criminal, civil and
administrative hearings
Forensic Science Specialties
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Criminalistics
Firearms and tool
mark examination
Document
examination
Fingerprint
identification
Forensic photography
and image analysis
Computer forensics
Forensic Science Specialties
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Forensic pathology
Forensic odontology
(forensic dentistry)
Forensic anthropology
Forensic toxicology
Forensic psychiatry
Forensic psychology
(includes criminal
profiling)
Criminalistics
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Drug chemistry
Trace evidence analysis
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Hairs and fibers
Glass and soil
Paint and plastics
Ignitable liquids (arson
accelerants)
– Explosive residues
– Gunshot residues
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Forensic biology
Forensic molecular
biology (i.e. DNA
profiling)
Types of Evidence
Testimonial
Documentary
Demonstrative
Physical
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
Types of Physical Evidence
Pattern
evidence
Trace evidence
Pattern Evidence
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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
Amido Black
Crowle’s Stain
Hungarian Red
Coomassie Blue
Fluorescence of Hungarian Red (under green light)
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
The Locard Exchange Principle
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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.’
Types of Trace Evidence
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Solid aggregates
– Fibrous (hairs, fibers, botanical samples)
– Particulate (glass, soil, metal fragments,
paint chips and smears, explosive
residues, gunshot residues)
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Liquids
– Blood, semen and other body fluids
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Molecular traces
– Explosive residues, ignitable liquid
residues
Forensic Analysis of Particulate
Trace Evidence
 Microscopic
examination
 Instrumental
methods of
analysis as
appropriate
Infrared Microscopy Combined with FourierTransform Infrared Spectrometry
Infrared Spectra of Artificial Hair
Strands
The Jeffrey McDonald Case
Forensic Biology and Forensic
Molecular Biology
Body Fluids Examined in the Forensic
Science Laboratory
Blood
 Semen
 Saliva
 Urine
 Feces
 Perspiration
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Screening Suspected Bloodstains
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Is that red-brown
stain a bloodstain?
If it isn’t blood we
don’t want to include
it in our blood
spatter analysis
If it isn’t blood we
don’t want the
forensic biologist to
waste time
processing it as blood
evidence
Forensic Analysis of Suspected
Bloodstains
Presumptive tests
 Confirmatory tests
 Species identification tests
 DNA profiling
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Human Erythrocytes
Commercial Blood Test Kits
Peroxtesmo
Hemastix
Luminol
Luminol
Confirmatory Tests for Blood
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Takayama test
– A crystal test for hemoglobin
– Pink, leaf-like birefringent crystals are formed
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Microspectroscopy
– Identifies the characteristic absorption spectrum
of hemoglobin
Takayama Crystals
Takayama Crystals
Human Blood Identification
Hexagon OBTI
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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
DNA Profiling
Structure of DNA
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DNA (deoxyribonucleic acid) is composed
of three components
– Phosphate groups
– Sugars (deoxyribose)
– Bases
» Adenine (A)
» Thymine (T)
» Guanine (G)
» Cytosine (C)
Double-Stranded (Duplex) DNA
Mutations
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The genetic information in DNA can be changed
by mutations
– Point mutations (one base substitutes for another)
– Insertions
– Deletions
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Natural selection constrains the variability of
functional DNA (i.e. genes)
‘Non-functional’ DNA has greater variability
DNA Extraction
Remove cellular material (cell membranes,
proteins etc.)
 Dissociate nuclear DNA from histones
 Purify DNA
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Types of Samples
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Body fluids
– Blood
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Tissues
– Muscle
– Bone
– Teeth
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Body fluid stains
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Bloodstains
Semen stains
Saliva stains
Urine stains
PCR – The Molecular Xerox
Machine
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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.
The CODIS System
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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
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
Nuclear DNA STR data
DNA Databases
Cases Aided by CODIS
DNA Databases
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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
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The UK’s ten locus STR database uses eight
of the thirteen loci used in the CODIS
database
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
Mitochondrial DNA Sequencing
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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
Mitochondrial DNA Sequencing
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
Advantages and Disadvantages of
MtDNA Sequencing
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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)
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Due to size of mtDNA database frequency
estimates are not possible
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
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Education
– BS in Chemistry (Emory
University)
– AM (1968), PhD (1976) in
Chemistry (Harvard
University)
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Forensic Science
Experience
– 1969-1971 Forensic
chemistry specialist, US
Army Criminal
Investigation Laboratories
(drug chemistry and
forensic serology)
– US Army CID investigator
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
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We offer the Master of
Forensic Science degree
Students may specialize in
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Crime Scene Investigation
Forensic Chemistry
Forensic Molecular Biology
Forensic Toxicology
High Technology Crime
Investigation
– Security Management