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What is Forensic Science
INTRODUCTION TO
FORENSIC SCIENCE

N. Zeynep Atay
Department of Chemistry
It is the application of Science to
Criminal and Civil Laws
HISTORY OF FORENSIC SCIENCE
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CRIME SCENE
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Forensic Science begins at the crime scene.
Finished-sketch diagram of a
crime scene. Courtesy Sirchie
Finger Print Laboratories, Inc.,
Youngsville, N.C.,
www.sirchie.com.
Criminalistics by Richard Saferstein
Prentice Hall
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SERVICES OF THE CRIME LABORATORY
MODERN CRIME LABORATORIES
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CRIME LABORATORIES AND
THEIR ORGANIZATION
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OPTIONAL SERVICES PROVIDED BY FULLSERVICE CRIME LABORATORIES
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Toxicology Unit
Fingerprint Unit
Polygraph Unit
Lie-detector
Voiceprint Analysis Unit
Crime-Scene Investigation (CSI) Unit
Physical Science Unit
Biology Unit
Firearms Unit
Document Examination Unit
Photography Unit
FUNCTIONS OF THE FORENSIC
SCIENTIST
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Analysis of physical evidence
Expert Witness
Training of staff in the proper recognition,
collection, and preservation of physical
evidence
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Forensic Pathology
OTHER FORENSIC SCIENCE SERVICES
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Forensic
Forensic
Forensic
Forensic
Forensic
Forensic
Pathology
Anthropology
Psychiatry
Odontology
Engineering
Computer and Digital Analysis
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Involves mainly the identification and examination of
human skeletal remains.
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Examination of bones may reveal sex, approximate
age, race and skeletal injury.
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Especially helpful identifying victims of a mass
disaster, such as a plane crash, through the collection
of bone fragments.
By investigating the stages of decomposition
of the body, time of death can be estimated.
Forensic Entomology
Forensic Anthropology
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Involves the investigation of sudden,
unnatural, unexplained or violent deaths by
either observation or through an autopsy.
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Study of insects and their relationship to criminal
investigation.
After decomposition begins, insects such as blowflies
start infesting the body, laying their eggs in human
remains, and ultimately hatch into maggots, etc.
Entomologists can identify these insects and
approximate how long the body has been left
exposed by examining the stages of fly larvae.
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Forensic Psychiatry
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A specialised area which investigates the human
behaviour and legal proceedings.
For civil cases, they determine whether the person is
competent to make decisions on wills, etc.
For criminal cases, they evaluate behavioral
disordersand determine competence to stand trial.
Criminalistics by Richard Saferstein
Prentice Hall
Forensic Odontology
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Helps identify victims through dental remains when
the body is in unrecognizable state.
Teeth are composed of enamel, the hardest
substance in the body. Due to the resilience of
enamel, the teeth outlasts tissues and organs as
decomposition begins.
Dental records can be compared to the suspected
victim.
Bite-mark analysis is also important in identifying
the suspect.
Forensic Engineering
Accident scenes are examined, photographs
are reviewed, mechanical objects are
investigated.
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How did an accident or failure happen?
Were the parties involved responsible?
If yes, how were they responsible?
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Forensic Computer and Digital Analysis
A new and fast growing field that involves
identification, collection, preservation and examination
of information derived from computers and other
digital devices such as mobile phones.
Common Types of Physical Evidence
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PHYSICAL EVIDENCE
“Physical Evidence can provide a link
between a crime and its victim or a
crime and its perpetrator”
Fingerprints (a classic identifier)
Blood, Semen and Saliva – these are subject to
serological and biochemical analysis (all contain DNA)
Documents – any handwriting, typewriting, ink,
indented writing, obliterations, burned or charred
documents (letters and e-mails link people)
Explosives – any device with an explosive charge
and any item that might contain the explosive residue
A fingerprint exhibit illustrating the matching
ridge characteristics between the crime-scene
print and an inked impression of one of the
suspect’s fingers. Courtesy New Jersey State Police.
Criminalistics by Richard
Saferstein
Prentice Hall
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Friction Ridges
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Every person has minute raised ridges of skin on the
inside surfaces of their hands and fingers and on the
bottom surfaces of their feet and toes, known as
'friction ridge skin'.
The friction ridges provide a gripping surface - in
much the same way that the tread pattern of a car tyre
does.
Friction ridge skin is also the only skin on the body
without hairs.
Fingerprint ridge characteristics. (Courtesy Sirchie Finger Print Laboratories, Inc.,
Youngsville, N.C., www.sirchie.com.)
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Fingerprint Ridge Characteristics
150 different ridge characteristics = minutiae (trivial
details)
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How many fingerprint points must match in
order for the fingerprints to be said to be
identical?
UK → 16 pts.
New Zealand and Australia → 12 pts.
India → 8 pts.
USA → each state has its own standard
FBI uses 12 pts.
There is really no scientific basis on how
many points should be matched!!!!
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The Principles of Fingerprint Identification
Uniqueness:
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No two friction ridge patterns are identical, whether they are on
different fingers of the same person or on the fingers of different
people. (The same principle covers all friction ridge skin.)
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While this principle is difficult to prove empirically, no two fingerprints have
ever been found to be identical in over a century of the use of
fingerprinting.
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Friction ridge patterns do not change naturally during the life of a
person.
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The pattern of minutiae starts developing in the third month of pregnancy
and is fully formed by the fourth month.
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During a person's lifetime, the pattern remains the same, apart from
changing in size or by accident, mutilation or skin disease, until death.
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In fact, the friction ridge patterns will remain after death until the
body decomposes.
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POWDERS
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Powder And Tape –
Probably the most well-known method of detecting latent prints
is dusting for them. A variety of powders are used in dusting for
prints, many containing aluminium or carbon. This finely crushed
powder is gently applied to a surface, and the minute particles of
powder cling to the print residue, making it visible to the human
eye. These prints are then lifted using adhesive tape.
Additionally, studies have demonstrated that while identical twins share the
same DNA profile markers, they can nevertheless be differentiated by their
fingerprints.
Drugs
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Brush it with
aluminum powder
The marks became visible.
Put a black rubber
lifter on it.
Marijuana
The marks are on
the lifter.
Put a plastic sheet over it.
Ready to search!
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Fibers – any fiber that might show crosstransfer between object and/or persons
(can link suspect and crime scene)
Ice-methamphetamine
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Hair – animal or human hair
showing cross-transfer (hair can be
matched microscopically)
DOG HAIR
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In humans, pigment
granules are commonly
distributed toward the
cuticle as shown in top
figure, except in redhaired individuals as in
bottom figure.
Animal hairs have the
pigment granules
commonly distributed
toward the medulla, as
shown in the figure.
CAT HAIR
Forensic Science CommunicationsJuly 2004 –
Volume 6 – Number 3
Forensic Science CommunicationsJuly 2004 –
Volume 6 – Number 3
Photomicrograph of Human Hair Root
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Wineglass-shaped root (deer family)
The root of human
hairs is commonly
club-shaped,
whereas the roots
of animal hairs are
highly variable
between animals.
Forensic Science CommunicationsJuly 2004 –
Volume 6 – Number 3
Forensic Science CommunicationsJuly 2004 –
Volume 6 – Number 3
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UNLESS DNA analyses are carried out:
Class Evidence: Hair
Body area from which the hair originated:
Scalp hair:
  little variation in diameter
  Uniform pigment distribution
  Might be dyed
Pubic hair:
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Short and curly
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Variable cross-section diameter
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Continuous medullae
Beard hair:
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Coarse
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Triangular cross-section
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Blunt (not sharp) tips from shaving and cutting
UNLESS DNA analyses are carried out:
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Age:
  Age of an individual cannot be learned with any certainty except
for infant (baby) hair.
  Infant hair:
  Short
  Undeveloped in character
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Sex:
Hair gives no indication of the sex of the individual from which it
came.
Common Types of Physical Evidence
(continued)
Glass
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Particles that may show cross-transfer or panes that
might have bullet holes (fragments are easy to
compare)
Two bullet holes in a piece of glass. The left hole
preceded the right hole
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Firearms and Ammunition – discharged or
intact
Impressions – tire markings, shoe prints,
depression in soil, glove or fabric impressions,
bite marks in skin or food, as well as knife cuts
Criminalistics by Richard Saferstein
Prentice Hall
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Purpose of the Examination of Physical
Evidence
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Identification:
Determination of the
physical or chemical
identity of a
substance with as
near absolute
certainty as existing
analytical techniques
will allow.
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Comparison: Subjecting a
suspect specimen and a
control specimen top the
same tests for the ultimate
purpose of proving
common origin.
(Comparing two or more
samples to see they
match.)
Comparison:
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If any of the selected properties are not alike, the scientist will declare
that the two items are not from the same source.
However, if all the selected properties match, they still may not be
able to conclude that the two specimens are from the same source
with 100% accuracary.
Hence, usually only the probability that two specimens came from
the same source is given.
Identification:
Typical tests for identification:
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Drug analysis
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Species determination
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Explosive residue analysis
Drugs: Testing the composition of a white powder may show that it is
illicit or prescription drug. Scientists need to determine what type of
drug it is: heroin, cocain or barbiturates, or a commonly used drug!
Fibers: In case of suspected arson, fragments of cloth, found where
the fire officers believe the fire might have started, could have petrol
residues lingering in the fabric.
Characteristics of Physical Evidence
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Individual: Associated with
a “single source” with
extremely high probability
Examples:
Fingerprints
Bullet Striations
Footprints
DNA
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Class:
Associated
with a “class” with high
probability, but
associated with a “single
source” with low
probability.
Information can be
gained by looking at the
“class” of an item.
Example:
Hair
Blood type (O, A, B, AB)
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Class Evidence: Hair
Class Evidence: Hair
Body area from which the hair originated:
Scalp hair:
  little variation in diameter
  Uniform pigment distribution
  Might be dyed
Pubic hair:
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Short and curly
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Variable cross-section diameter
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Continuous medullae
Beard hair:
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Coarse
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Triangular cross-section
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Blunt (not sharp) tips from shaving and cutting
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Age:
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Age of an individual cannot be learned with any
certainty except for infant (baby) hair.
Infant hair:
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Short
Undeveloped in character
Sex:
Hair gives no indication of the sex of the individual
from which it came.
Sources of Biological Evidence
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Blood
Semen
Saliva
Urine
Hair
Teeth
Bone
Tissue
The probability of 2 people having the same fingerprint is 1 in 1x1060
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Human Identity Testing
DNA Use in Forensic Cases
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Most are rape cases (>2 out of 3)
Looking for match between evidence and
suspect
Must compare victim’s DNA profile
Challenges
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Forensic cases -- matching suspect with evidence
Paternity testing -- identifying father
Historical investigations
Missing persons investigations
Mass disasters -- putting pieces back together
Convicted criminal DNA databases
• Mixtures must be resolved
• DNA is often degraded
• Inhibitors to PCR are often present
CODIS
CODIS (Combined DNA Index System) is a
computer software program developed by
the FBI that maintains local, state, and
national databases of DNA profiles from
convicted offenders, unsolved crime scene
evidence, and profiles of missing persons.
Thank you for your
attention!
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