Download Forensic Science – Optional Module

Forensic Science Unit
Science IV: Optional Unit
2014
Adult Learning Program: Science IV
Forensic Science – Optional Module
Start Date:
Anticipated Finish Date: ______________Actual: _______________________
Area
To do
Value
1. Paper Chromatography &
Handwriting Analysis
10
2. Hair and Fiber Analysis
10
3. Blood Typing
10
4. Fingerprinting
10
5. Fingerprinting: Multiple
Methods
10
6. Blood Splatters / Stains
10
Research report on topic of your
choice (your choice of
presentation mode)
10
Case
Study
Crime Scene
Investigation
30
Test
Based on lab work and theory
from module
20
Labs
(You must
complete a
minimum of 4)
Report
(option or
complete 5
labs)
Actual Mark
CLASS SCHEDULE – If you have chosen this module, then you have
committed to attending all classes and labs. We will move through this module as
a group. If you miss a lab in your scheduled time, it is your responsibility to make
it up in the other time slot. The only flexibility of time is in the writing of the test,
though you are encouraged to have taken this test no later than January 31. In
the event that the weather plays havoc on the schedule, a new schedule will be
developed and circulated.
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Table of Contents
Introduction ......................................................................................................................... 3
Learning Outcomes ............................................................................................................. 3
History of Forensic Science ................................................................................................ 4
Firearms and Toolmark Identification ................................................................................ 5
Document Analysis ............................................................................................................. 6
Explosives – Fires & Bombs............................................................................................... 9
Microscopy in Forensics ................................................................................................... 11
Blood Analysis .................................................................................................................. 13
DNA Analysis ................................................................................................................... 15
Fingerprinting ................................................................................................................... 17
Blood Splatter / Bloodstain ............................................................................................... 19
Other Testing Methods ..................................................................................................... 19
Resources .......................................................................................................................... 23
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Introduction
People working in the field of Forensic Science use scientific knowledge and apply
scientific theories to help them to solve crimes. Forensics draws from many disciplines
of science. Blood grouping, DNA fingerprinting, chromatography, chemical analysis of
various substances, microscopic observation, entomology and radioactive dating are a
few of the techniques used to prove when, where, how and by whom a crime is
committed. This unit will help you to understand how concepts from science,
particularly those from biology and chemistry, are useful to scientists and investigators in
the course of their work.
Learning Outcomes
After completing this unit, you should be able to
 Define Forensic Science.
 Examine the history of forensic science, noting important developments.
 Explain the connection between developments in technology and developments in






forensics.
Describe the operation of a variety of testing methods in forensics
Understand and explain the role of DNA analysis in forensic science.
Understand and explain the importance of microscopy in Forensic science.
Compile and interpret pieces of evidence to solve a simple crime.
Administer a fingerprinting process and identify fingerprint patterns
Compare methods of explosives detection.
NOTE:
There will be a number of lectures explaining information in this module. A
schedule of these lectures will be posted. It will be very helpful to you to attend
these lectures as they will review the lab procedure the day before the lab takes
place and will give you the opportunity to ask questions concerning any
information in the module you do not understand or find confusing. Labs are
scheduled and under regular circumstances, will not be repeated. The case study
day is 30% of your mark for this module and has only be repeated in the same
year once – this was because of a Metro Transit Strike.
Excellent attendance is critical to successfully completing this module. If daily
attendance is problematic for you, you may wish to consider completing an
alternate module as one of your elective modules.
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History of Forensic Science
In Canada
Prior to 1953, efforts in forensic science in Canada generally occurred independently of
each other. News of progress in the area was usually heard through the media.
It wasn't until October 16, 1953, that seventeen people interested in developing the field
met in Ottawa to form the Canadian Society of Forensic Science. These people were led
by RCMP firearms identification expert Inspector James Churchman, and chemist Dr.
Charles Farmilo with the Department of National Health and Welfare. Beginning in 1963
the society began to publish a newsletter. Then in 1968, the society began publication of
the Canadian Society of Forensic Science Journal. Today membership is over 450. For
more information on the beginnings of this society and its founding members, see your
teacher for a supplemental reading.
The first forensic laboratory in North America, the Institut de médecine légale et de
police Scientifique, was established in Montreal by Wilfred Dérôme in 1914. In the early
twenties, this laboratory developed a method of determining the alcohol content of blood.
The method was problematic, and had to be modified so many times that the event went
unappreciated for its historical significance. The Institut gained more recognition from
outside the country than from within Quebec and Canada. In 1922, Dr. Rosario Fontaine,
graduate of a diploma in legal medicine from University of Paris, joined the Institut.
In 1932, the government of Ontario hired Dr. E. R. Frankish to organize and operate a
laboratory that would perform autopsies, blood tests, and the examination and analysis of
seminal stains, hairs, fibers, and plant materials. Blood and urine analyses were added
later.
Other Milestones
The first record of a print being involved in a crime was in the year 1000 BC. A Roman
attorney showed that a palm print was used to frame a person for murder.
The 1880s saw the development of fingerprint identification. This would soon become a
key in forensic crime-solving for investigators. In 1823 the first classification of
fingerprints was established by a Prussian, Johannes Purkinje. In 1880 Scottish physician
Henry Faulds used powders to increase the visibility of fingerprints, and this became
common practice in solving crimes.
In 1901 a new classification of fingerprinting was developed as a revision of the previous
system. This work was completed by Sir Edward Henry of Scotland Yard. 1903 saw
fingerprints identifying which individual out of a set of twins was guilty of the crime. In
1964, Scotland Yard’s Fingerprint Bureau started the computerization of the nation’s
fingerprints.
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Throughout this document you will note other milestone developments in forensic
science. The two websites http://www.forensicdna.com/Timeline.htm and
http://www.troopers.state.ny.us/ForSc/ForScHist/ForScHistindex.html also provide links
to other information on the history of forensic science.
Firearms and Toolmark Identification
Investigators must look closely at the "tools" of crime if they are to verify that they have
been used. Firearms and toolmark identification involves determining what make of gun,
other type of weapon or type of explosive was used in the crime being studied. As well,
they look at imprint evidence. In all cases the use of microscopes is critical to
establishing solid evidence.
Bullet Matching
When firearms are made, they undergo a process called rifling. The purpose of rifling is
to cause the bullet to spin as it passes out of the barrel of the firearm. This spin enables
the bullet to travel in a straight line. Rifling is a series of ridges (called lands) and
grooves (called groves) along the inside of the gun barrel. As the bullet passes out of the
barrel these lands and groves place microscopic marks on the bullet. The bullet can be
scarred in this way because it is made of lead. Lead is a soft metal, and becomes softer as
a result of the heat generated inside the gun when it is fired. As well, friction occurs
when the bullet passes through the barrel.
Each firearm creates unique markings (much like human fingerprints) on the bullets fired
from it. Because of this, scientists can match a spent bullet with a particular gun. A new
bullet can be fired from the gun, and the two bullets can then be compared under a
microscope. If after complete rotation of the two bullets, the scientists are unable to
perfectly match the bullet markings they know that gun found was not the one used in the
crime.
Imprint Analysis
Forensic investigators survey the scene of the crime for their clues. They comb all
surfaces for any imprints that may have been left by criminals. Imprints used as forensic
science evidence are of two types: two-dimensional (2-D) or three-dimensional (3-D).
2-D imprints are formed when an object passes through a substance and removes some
of the substance leaving a negative image of the object. This process can also leave a 2D imprint on another substance. One example that could happen at a crime would be if
one person stabs another and steps in the blood that is spilt. The offender will leave 2-D
imprints in the blood (negative image) and also across the floor or street where he/she
walks after stepping in the blood.
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3-D imprints are left in substances such as mud, wet concrete or plaster. In this
situation, the object pushes into the imaging substance and leaves an image that includes
the surface relief (bumps and hollows, tread pattern and wear, etc.) of the object. As the
imaging substance (mud, wet plaster, etc.) dries, the image of the object remains. The
unique wear patterns on tires and footwear can then be used to identify the vehicle /
person who made the print.
Toolmark Identification
It is possible for crime investigators to identify the actual tool that was used in a crime
(not just the make or model) from the markings it leaves. If a detective sees that a
screwdriver was used to gain unlawful entry into a building, he or she knows that the
marks it leaves on the lock or doorway are unique to that screwdriver. The manner in
which the tool scraped the surface and /or its defects may not be easily distinguished by
the naked eye, but will be visible and identifiable under microscopic examination.
Document Analysis
This branch of forensic science uses the knowledge of experts in several areas. Some of
those areas are handwriting analysis, typewriting analysis, paper analysis, counterfeiting,
forgery, computer print-out and diskette analysis, ink analysis and document dating.
Handwriting Analysis
Handwriting analysis involves painstaking examination of the design, shape and structure
of handwriting to determine authorship of a given handwriting sample. The basic
principle underlying this type of analysis is that no two people write the exact same thing
in the exact same way. Every person develops unique peculiarities and characteristics in
their handwriting.
Handwriting analysts must examine a number of characteristics of the words written.
These characteristics include letter formations, connecting strokes between the letters,
upstrokes, retraces, down strokes, spacing, baseline, curves, size, distortions and
hesitations. By examining these details and variations in a questioned sample and
comparing them to a sample of known authorship, they can determine whether or not the
authorship is genuine. Experts use magnifying lenses and microscopes to examine the
subtle differences in handwriting samples – especially when dealing with a people highly
skilled in forgery. Accurate and precise measurement is key to the success of this
analysis.
You should note that this type of handwriting analysis is not to be confused with studying
handwriting to determine someone's personality traits. This type of study of handwriting
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is not considered true science by those in the forensics field but can also be considered
when trying to gather information on the personality and mental attitude of a suspect.
Ink Analysis
When examining documents such as a ransom note, crime investigators will analyze the
ink. All inks are not equal. Though we are able to distinguish one blue ink from another
by looking at it, a forensic scientist is able to tell more. The scientist is actually able to
distinguish one ink source from another. One method of analyzing ink is through a
method known as ink chromatography.
Ink is a mixture of several colors used to produce one. Chromatography is a method used
to separate and identify parts of a mixture. Using chromatography, the colors in ink can
be separated.
If ink is exposed to certain liquids called solvents, the colors will dissolve and separate
within the liquid. If the solution is then allowed to soak into a piece of chromatography
paper, the different colors will create bands on the paper. They will remain in solution.
Inks of the same type will always produce the same banding pattern when this technique
is used. The bands are created because the different components of the ink dissolve
differently in the solvent used. This is referred to as the ink's solubility.
The greater the solubility of the ink for the solvent, the further up on the paper the band
will appear. The higher band results because the ink component stays dissolved in the
solvent for a longer period of time than other components, and travels further up the
paper. The resultant paper with bands on it is called a chromatograph.
Chromatography is a scientific concept that allows a crime investigator to uncover
information that would be missed by the naked and untrained eye.
See diagram below for a sample of a typical paper chromatograph.
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Typical Paper Chromatograph
End solvent
line
Ink
Spot
Separated ink
components
Intermediate
Complete Lab 1: Chromatography and Handwriting Lab
Typewriters
As with other types of tools, all typewriters of a particular make and model are very
much the same. However, with time and use, individual models develop defects that
translate to paper when the machine is used. These defects on the typed page can be
matched back to the typewriter that was used to create it.
These defects in the typeface are revealed in a number of ways. If the type bar (the bar
on which the letter element is attached and hammered down to the page) is bent, the letter
is misaligned or 'off its feet.' Misalignments can also cause an area of a specific letter not
to print, such as the loop on the bottom of a 'g.' The letter can be misaligned or damaged
horizontally or vertically. Small lumps of plastic can adhere to the type key during
manufacture and are made permanent by the coating process. This defect is called
'flashing.' As wear and tear increases, the defects become more exaggerated.
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Printers
As with the typewriter, printers of the same make and model produce printouts that
appear identical. Closer examination of these documents, however, will show that each
individual computer printer produces a document unique to it.
Laser printers produce a document by burning carbon toner (powder) onto the paper.
The paper is rolled over a barrel to produce this image. With wear on the barrel, the
barrel will develop markings unique to itself. For example, while performing regular
maintenance on the barrel a technician may accidently create a small groove in the barrel.
Any characters that come in contact with that part of the barrel will have an image that is
slightly distorted.
Inkjet printers create documents by spraying ink onto the paper. Again with wear and
tear - perhaps the results of maintenance and rough use - the printer will develop unique
quirks. The wear and tear may result in the spraying mechanism being slightly damaged.
The mechanism is still able to function but may not create characters that are as perfectly
shaped as they were when new.
Dot matrix printers have hammers that strike an inked ribbon that strikes the paper to
create an image. The hammer creates a small dot on the paper and creates characters by
grouping the dots together. As the printer is used the hammers will develop patterns
unique to the printer. Close examination of the dots will reveal that not all are perfectly
round as they were in the beginning.
Analyzing the printout will tell investigators what type of computer printer has been used
- laser, inkjet or dot matrix. Analyzing the ink will tell investigators what type of printer
they are searching for. Different manufacturers use different ink compositions. This is
particularly useful for inkjet printers.
Explosives – Fires & Bombs
If an investigator proves that arson has been committed, the chances are that the fire was
set by the criminal as a way of destroying property or murdering someone. However,
fires may also be the result of accidents. When fire inspectors investigate a fire, often the
first thing they need to do is to determine if the fire was an accident, or deliberately set.
Fire (burin) is a chemical reaction. It is known as combustion – the chemical
combination of a substance with oxygen. All elements have a characteristic flame colour
when they burn. In chemistry it is referred to as a flame test. Some compounds also
produce characteristic colours of flames and smoke. For example, if a fire has started
because some cooking has ignited, the flames will be yellow and the smoke brown. On
the other hand, if the cause of the fire has been gasoline the flames will be yellow or
white with black smoke. Compounds are not as specific in their flame colour as are
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elements, but knowing the colour of the flame and smoke is useful to investigators. This
information can help them narrow their search for the cause of the fire.
If the fire being investigated is the result of arson, one sign that points to this is the
presence of more than one starting point for the fire. The starting point for a fire is called
the seat of a fire.
Other indicators of arson are the presence of accelerants, piles of flammable materials, a
fuse or timing device. One problem investigators run into when trying to detect
accelerants is the presence of carpet in the area that has been burned. When some types
of carpet burn they give off by-products that are very similar to some common
accelerants. For this reason, any unburned carpet samples at the site will be taken back to
the lab and burned to analyze any by-products.
There are two broad categories of accelerants – petroleum distillates and non-petroleum
accelerants. The most common of the petroleum accelerants are gasoline and kerosene.
Common non-petroleum accelerants are turpentine, lubricants and alcohol.
Investigators attempting to identify the accelerant investigators often use dogs –
particularly the Labrador Retriever. This breed of dog has the most sensitive sense of
smell of all dogs. The dog is trained to detect the smell of several common accelerants.
For more information on this topic you may wish to consult the website
http://www.arsondogs.com/.
Another method fire investigators use to detect accelerants is to use ultraviolet light.
When exposed to UV light, petroleum-based accelerants will glow.
Another concern when it has been determined that the fire being investigated is the result
of arson is the reason for the arson. If a body is found in the ruins of the fire,
investigators must then determine if the person was killed before the fire was lit, or if
they died as a result of the fire. This is generally determined during an autopsy.
Forensic scientists analyze samples of the victim’s blood and lungs using a microscope.
If soot is discovered in the lungs, the conclusion is that the victim was alive and inhaled
smoke when the fire began to burn. Similarly, if the blood is found to contain higher than
normal concentration of carbon monoxide, this too suggests the body was alive when the
fire was started.
Burning rarely occurs to the degree that would conceal other injuries to the body. If a
wound was inflicted on a person previous to the burning, there will be a mass of white
blood cells evident at the site of the wound. This indicates the body was already in the
process of trying to ward off infection from the injury. These white blood cells will
blister when burned. In contrast, burns on a body that is dead before the burning will be
hard and yellow. When scientists use methods of detecting poisons and drugs (as
described below) a burned body is still able to disclose if it was poisoned.
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Microscopy in Forensics
Microscopes continue to be one of the most important tools in forensics. Various types
of microscopes are used in various types of analyses.
Light Microscope
This microscope uses the visible light spectrum for its illumination source. The use of
lenses enables the examiner to magnify the specimen up to 1500 times its size. This type
of microscope is useful in examining hair fiber and bullet samples. Cameras are mounted
to the eyepiece of light microscope to gather a permanent image of the sample.
Electron Microscopes
There are two types of electron microscopes – transmission and scanning. Both types of
electron microscopes use a beam of excited electrons for their illumination source.
In the transmission electron microscope (TEM), the beam of electrons passes through the
specimen.
The scanning electron microscope (SEM) passes the beam of electrons over the surface
of the specimen. An electron gun at the top of the SEM chamber generates a beam of
activated electrons. This beam passes down the chamber and is focused on the specimen
using magnets. The beam then scans back and forth over the object. As the beam passes
over the object, some electrons are reflected back. These are called back-scattered
electrons. An electron detector senses these reflected electrons and amplifies their
reading to generate an image. The image may then be produced on a monitor or
photographic film.
Magnification with a SEM can be up to 100, 000 X and can also provide information
about the elements that are present in the sample being examined. Because of its ability
to provide information about the elements composing a substance, the SEM is a useful
tool when analyzing paint samples, gunpowder residue, other types of explosives, soil
samples and any other substances found at a scene that are foreign to that scene.
For an online demonstration of how the SEM works, check with a web site such as:
http://mse.iastate.edu/microscopy/path2.html, http://www.mos.org/sln/SEM/works.html,
or perform your own search using the words “Scanning Electron Microscope.”
Hair and Fiber Analysis
Scientists first examine hair with a microscope to decide if the hair is human or animal.
To the naked eye, a long blonde hair from a golden retriever or one from its owner can
look very much alike.
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To determine if the hair is human or animal, the forensic examiner will pay attention to
the outer-most layer of the hair – the cuticle. The cuticle has scales that overlap. These
scales allow the examiner to determine the species to which the hair belongs.
Inside to the cuticle is the cortex. This layer contains the pigment molecules that will
give the hair its colour. Arrangement of pigmentation within the cortex differs from one
person to the next. By examining this, the investigator can tell if the person has
chemically coloured their hair.
The very centre of the shaft is known as the medulla. This part of the hair is also
important when determining species.
Examination of hair can help in establishing the racial group of an individual, or their
approximate age. Adult hair is much coarser than children's hair. Without attached
follicle tissue (the white bulb attached to the root when a hair is pulled out), it is not
possible to perform DNA analysis on a hair sample.
Hair analysis can prove helpful in solving crimes because hair can contain poison residue
if the body has been subjected to poisoning. Also, traces of dirt can help investigators
identify the location of a crime if the sample in the hair is not characteristic of the area in
which the victim is found.
There is some variation in different hairs from the same person. Investigators prefer to
use a number of hairs as opposed to a single hair for this reason.
Fibers are the smallest unit of a textile material. Fibers are useful as they are often able to
establish the presence of another person at a crime scene. They have also been useful in
establishing the location of the crime when the body has been moved.
Scientists examine fibers under a microscope in the hope of discovering a unique
characteristic of that fiber. This may be a particular pattern of the dyeing process,
twisting patterns, or some unusual shape to the fiber. The presence of a characteristic
unique to the fiber is the benefit of using fibers in crime solving. The uniqueness of the
fiber helps to establish (or dispute) the connection between the suspect and the crime.
Complete Lab 2: Hair and Fibre
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Blood Analysis
The basic level of blood analysis will involve determining the types of blood present.
Blood type is an inherited characteristic. A person may have either type A, B, AB or O.
The protein(s) that determines if a person has type A, B, AB or O will be present or
absent in the red blood cells (RBC).
Each gene (location) for a characteristic found on one of the 46 chromosomes present in
the human cell can have a different form. The form of the gene is known as the allele.
For some characteristics or traits there are just two forms of the gene; for others there
may be more than two. The gene for blood type in humans has three alleles – LA, LB, LO.
The LA allele will code for the person to produce antigen A on the surface of their RBC.
The LB allele will code for the person to produce antigen B on the surface of their RBC.
The LO allele will code for the person to not produce antigens on the surface of their
RBC. The table below shows the possible combinations of genes a person may have,
known as the genotype, and the resulting blood type.
Allele from Allele from Child’s
Child’s
Mother
Father
Genotype Blood Type
LA
LA
LA LA
A
A
B
L
L
LA LB
AB
LA
LO
LA LO
A
B
A
A B
L
L
L L
AB
LB
LB
LB LB
B
B
O
B O
L
L
L L
B
LO
LO
LO LO
O
From the table you can see that there is more than one possible combination of genes for
the same blood type. When a person has an allele that results in the production of A
antigen on the surface of their RBC, the person will have type A blood if the second
allele is an A or an O. This is because the allele for A (and B) is dominant over the allele
for O. Dominance in genetics can be thought of as the allele being more powerful, as
black pigment in paint is more powerful than white – you can never add enough white
pigment to black paint to make it white. In the case of the allele for A antigens and B
antigens neither is dominant over the other, thus the blood type AB. The allele for type A
and the allele for type B are said to be codominant. Each is as strong as the other.
The dominance or recessiveness (opposite of dominance) of an allele does not indicate
that one of the traits is necessarily better than the other. It simply means that one form is
able to overshadow the other.
In addition to generating the coded antigen, blood also contains antibodies for the protein
the person is not coded to produce. The table below summarizes the blood type of a
person and the antibodies present in their blood for blood type proteins.
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Blood Proteins Antibodies
Type Present
Present
A
A
B
B
B
A
AB
A, B
None
O
none
A, B
An antibody is a blood component that is able to ingest and destroy a foreign substance or
organism. Thus type O blood will see the presence of type A and / or type B proteins as
being foreign material and attempt to destroy these proteins. This is the basis for blood
typing.
To determine a blood type a small sample of blood is needed. After the blood sample has
been obtained, a drop or two is placed on two microscope slides. One is then mixed with
anti-A and the other is mixed with anti-B solutions – the anti-A and anti-B antibodies. If
the blood mixed with the anti-A solution clumps (coagulates) then the person has type A
blood. The anti-A antibodies in the solution attacked the A proteins on the RBC surfaces
and tried to destroy them. The diagram below shows various results expected from this
type of blood testing.
BLOOD TYPING
Anti-A solution
Anti-B solution
Blood Type
A
B
AB
O
Establishing the blood type of the person who committed the crime helps to narrow the
field of suspects.
Complete Lab 3: Blood Typing
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DNA Analysis
DNA analysis is also referred to as “DNA Fingerprinting”. This technique was
developed in 1980 by Dr. Ray White, and DNA evidence was first used to convict a
criminal in 1987. This is a useful method of determining who committed a crime since a
person’s DNA is as unique to a person as their fingerprints. Identical twins are the
exception – their DNA is the same, but their fingerprints are different. The criminal’s
DNA is more likely to be found at the crime scene than are his or her fingerprints.
DNA is found in all cells of a person. Therefore, if a hair, a spot of blood, skin scrapings
from underneath the victim’s nails, or other sample from the criminal is recovered from
the crime scene, a definite identification of the criminal can be made.
DNA is an abbreviation for deoxyribonucleic acid. This is the material carrying our
genetic code. DNA resembles a twisted ladder. DNA is made from a number of smaller
molecules bonded together. There is a sugar molecule deoxyribose, a phosphate group
from phosphoric acid and a nitrogenous base. The nitrogenous base may be guanine,
thymine, adenine, or cytosine. The diagrams below show the structure of these
components of DNA.
The deoxyribose and the phosphate groups join to form the sides of the ladder with the
nitrogenous bases forming the rungs by joining together through the attraction of
hydrogen bonds. A hydrogen bond is the attraction of a hydrogen atom in one molecule
to a fluorine, nitrogen or oxygen in another molecule. The molecules involved in the
hydrogen bond are polar molecules. The diagram below shows the joining of
phosphoric acid with deoxyribose.
The phosphate –deoxyribose complex joins with the nitrogenous bases to form
nucleotides. The diagram below shows a nucleotide formed from the joining of thymine,
deoxyribose, and phosphoric acid.
The nitrogenous base nucleotides pair in specific combinations – adenine pairs only with
thymine and cytosine pairs only with guanine. The diagram below is a schematic
representation of an untwisted strand of DNA.
A
T
A
T
T
A
T
A
C
C
A
A
G
C
G
C
C
G
The sequence of the base pairs is how one person’s DNA differs from another's (except
for identical twins). Related family members have DNA combinations more similar than
people who are not related, but there are still significant differences.
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One method of DNA fingerprinting is using a process similar to that used in ink analysis
– paper chromatography.
In order to generate the DNA fingerprint, the DNA must first be extracted from the
evidence sample from the crime scene and cut into fragments. Cutting the DNA into
fragments is performed by restriction enzymes. These are special enzymes that are able
to separate the strand of DNA into shorter lengths at specific locations.
Next the DNA fragments are placed on a gel plate in a manner similar to placing the ink
spots on paper for paper chromatography. An electric current is run through the plate,
and this process is known as electrophoresis. For DNA analysis the negative connection
is nearest the end of the plate where the DNA fragments are originally placed. The
shorter fragments travel furthest on the plate. After this, the plate is placed in a blotter
apparatus.
The apparatus has a sponge on the bottom on which the plate is placed. Next there is a
nylon membrane, then paper towels and a weight. This transfers the DNA to the nylon
membrane as denatured single stranded DNA. The membrane is then incubated in the
presence of a DNA probe that is radioactive. The radioactive DNA probe bonds to its
matching DNA counterpart on the membrane. This membrane is then rinsed and placed
between two X-ray films. The radioactive probe then creates bands on the film. More
than one radioactive probe may be used in a given analysis situation. This process is
referred to as Southern Blotting. The diagram below shows results similar to those
expected with this type of DNA fingerprinting.
Control Control Victim Suspect Victim
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For animated presentation of this information search the Internet using the keywords
“DNA”+ "Fingerprinting” or check out a site such as
http://biology.about.com/gi/dynamic/offsite.htm?site=http%3A%2F%2Fvector.cshl.org%
2Fresources%2Faboutdnafingerprinting.html.
Fingerprinting
As noted above, except for identical twins, everyone has unique DNA. Everyone has
unique fingerprints – even identical twins. There are central banks of fingerprints in the
USA and Canada as well as in other parts of the world. There are four basic groups of
fingerprint patterns: arch, whorl, loops and composites (a mixture of two of the other
patterns). Each of these groups has subgroups. For diagrams of these patterns, check
with your teacher or a website such as http://www.fbi.gov/kids/k5th/whatwedo3.htm or
http://www.ridgesandfurrows.homestead.com/fingerprint_patterns.html or perform your
own search using keywords “Fingerprint Patterns”.
The process of taking fingerprints from fingers is relatively simple. Each finger is given
a number one to five starting with the right thumb, and then six to ten starting with the
left thumb. Each finger is coated with ink and then pressed on to a “ten-card” in the
appropriately numbered box on the card. When pressing the fingers it is important to roll
the finger from one edge to the other. In addition to the fingerprints, name, aliases, date
of birth, size of hand, shape of palm, eye colour and other relevant types of information
are included on a fingerprint card. For a sample of fingerprint cards used today contact
your local law enforcement or child find office.
Our bodies contain amino acids – building block molecules. Amino acids contain long
chains of carbon and hydrogen atoms joined together as well as an amino (nitrogen /
hydrogen) group and a carboxylic acid group. The diagram below shows the structure of
a simple amino acid – glycine.
Amino group
O
Carboxylic acid group
H
H2N
C
C
OH
H
Our bodies also produce perspiration by nature of our metabolism. Metabolism is the
continual breaking down of fuel molecules, mainly glucose, and building of other
materials – for example hair, nails and skin. When our amino acids combine with our
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sweat and we touch something, an image of our fingerprint is transferred to the object we
touched. This type of fingerprint is known as a latent print (not ordinarily visible to the
eye).
Investigators currently use a variety of methods for making latent prints visible. The
easiest latent prints to develop are those left on nonporous surfaces. The first method
used to retrieve these prints involved a gray-black dusting powder. This method is still
used today. It is most effective when the prints are fresh – the natural oils have not had
time to dry. The powder is gently brushed on with a soft brush and then excess is blown
away. The resulting images are photographed and also lifted with a special tape. The
tape is then applied to a ten-card to preserve the print. One disadvantage to using grayblack powder is trying to reveal prints on similarly coloured surfaces. Today other
colours of powders are available for use. Some powders have the ability to glow under
UV light.
Fuming is another method of obtaining latent fingerprints. In fuming, a chemical that
vaporizes easily is exposed to an item the investigators suspect to have latent fingerprints.
The chemical is able to chemically bond to the amino acids in the fingerprint thereby
emphasizing the print and making it possible to be photographed or lifted. Fuming with
super glue (cyanoacrylate) was discovered by accident when a British police officer used
some of the glue to fix a broken heater and realized how the prints on the heater became
visible. Normally fuming is done in a lab in an enclosed area. However, Super Glue
permits items that cannot be transported back to the forensic lab to be checked for prints
at the scene. After prints become visible using fuming, powder may be used on the print
so that it may then be lifted.
Though not the last, another important method of obtaining latent prints is vacuum metal
deposition (VMD). This method of fingerprint detection is expensive but will often
work where others have failed – even on surfaces that have been submerged in water.
The machine used exposes the fingerprint to gold vapours in a vacuum. The gold is
absorbed into the oils present in the print. The gold-coated print is then exposed to zinc,
which in turn bonds to any gold that has stuck to the print area. In 1989, the RCMP was
the only organization in North America to own this technology.
Complete Lab 4: Fingerprint Analysis and
Lab 5: Multiple Methods of Fingerprinting
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Blood Splatter / Bloodstain
Anytime blood is present at a crime scene, the crime is considered to have been violent.
As you have learned earlier in this unit, from a sample of blood suspects can be
eliminated or confirmed. In this section, you will learn how the patterns of blood found
at a crime scene can inform investigators about the events of the crime, the weapon(s)
used and the movement of those involved.
More information on blood splatters and bloodstains will be discussed in class. Be sure to
attend this class and get notes as it will help you in completing the “Blood Splatters and
Stains Lab.”
Lab 6: Bood Splatter lLab
Other Testing Methods
There are many other methods of testing and gathering evidence in the world of forensic
science. Some others that we will examine are spectrometry, atomic absorption
spectrometry, breathalyzer, drug testing, gas liquid chromatography and the polygraph.
Spectrometry
Spectrometry is the study of spectra for atomic and molecular structures. The
spectrum of a substance is the range of energy emitted from the substance. The range is
displayed in order according to wavelength. This is an effective means of identifying
substances because all elements have a unique spectra. Scientists use a spectrometer to
examine substances by spectrometry. For an illustration of a spectrometer, perform an
Internet search for the term or visit the web site
www.acp.edu/facultystaff/genchem/GC2/lab/spectro/spec202.htm. This site shows a
labelled diagram of a visible light spectrometer. Other models of spectrometers, though
similar in design, are able to measure energy outside of the visible spectrum.
FT-IR
One type of spectrometer frequently used by those involved in forensics is the Fourier
transform infrared spectrometer (FT-IR). The FT-IR has an infrared energy source
which provides the energy to be absorbed by the unknown substance. After the substance
has been hit by the IR energy, some of the energy will be absorbed and some will be
reflected. The reflected energy is recorded by the detector inside the machine. The
detector then produces a signal that is unique to that substance. A computer is then used
to “visualize” the signal. The information concerning the signal is then compared to
databases of spectra of known substances for the purpose of making a match. This
method of substance identification is a quick and accurate means of identifying narcotics,
bomb components or other materials. Your teacher has a short handout concerning more
information on FT-IR.
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Polygraph
The polygraph or lie detector is a testing procedure which most of us have heard about. It
often is presented in movies and TV shows. There are many jurisdictions that will not
accept polygraph tests as evidence. They are however often used as in conjunction with
other pieces of information.
The person being questioned is connected to the polygraph machine with a number of
connections
 Rubber tubes to the chest – measure respiration
 Blood pressure cuff on arm – measure blood pressure
 Metal plates on fingers – measure skin response
The person is asked some basic questions regarding their name, age, and address. The
purpose of these simple, neutral questions is to establish a baseline for the subject. The
machine records a mark on a paper when the subject answers each question. The theory
is that the subject will not give false answers to these questions. This will inform the
investigators of the subject’s normal blood pressure, skin temperature, respiration rate
and skin moisture level under the questioning conditions.
When we are stressed our bodies generate uncontrolled physiological responses. This is
the premise on which the polygraph is based. Once the baseline readings for the subject
are established, the interviewer then continues with asking questions related to the crime
being investigated. When telling lies, our bodies produce a greater physiological
response then when we answer with the truth. The polygraph will record rises in the
subject’s blood pressure, temperature, respiration rate, and perspiration on the skin. The
results will indicate one of three things: the subject is truthful, the subject is deceptive, or
the results are inconclusive.
The nerves that control the responses being measured by the polygraph are part of the
autonomic nervous system. This section of our nervous system controls involuntary
responses to our environment. The autonomic system in turn is divided into the
sympathetic and parasympathetic systems. The sympathetic system prepares the body
for increased activity. This is the system that is activated when we are stressed.
The nerves controlling the sympathetic system begin in the spinal cord and transmit their
signals outward to there target organs. The stress of telling a lie stimulates the release of
acetylcholine by preganglionic nerves of the sympathetic system in the spinal cord.
This chemical travels across as small gap known as a synapse to the dendrites of postrvganglionic nerves belonging to the sympathetic nervous system, and the system
becomes activated. The impulse travels from the dendrites to the cell bodies and then
down the axons to the nerve end bodies. The end bodies contain vesicles (sacs)
containing another chemical messenger. The chemical messenger or neurotransmitter
released by most sympathetic nerves is noradrenaline. This neurotransmitter will
stimulate heart rates and respiration rates, as well as perspiration rate. A visit to the
website http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/P/PNS.html#sympathetic
will provide more detailed information on this topic if you are interested.
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Authorities continue to debate the validity of a polygraph test. According to the
American Polygraph Association, the test is valid. The problems encountered with the
test are in the administration of the test. If the polygraph tester is not properly trained,
the accuracy of the test will be jeopardized. The website
sorrel.humboldt.edu/~klm28/polygraph.html is one site to consult to see a picture of a
typical polygraph machine and a sample of its printout results.
Breathalyzer
The Breathalyzer was invented by Dr. Robert Borkenstein in 1954. It uses a breath
sample to determine the level of alcohol in a person’s system. When a person drinks
alcohol some of the alcohol is absorbed in the mouth, throat, stomach and intestines into
the bloodstream. Once in the bloodstream, alcohol is able to travel to all parts of the
body. When it reaches the brain and other parts of the central nervous system, alcohol
acts as a depressant by slowing down the functioning of the nerves.
Alcohol is composed of a group of chemicals. The alcohol normally consumed is
ethanol. Alcohol ingested through the mouth is able to enter the bloodstream unchanged.
Ethanol is able to vaporize in the lungs, and some exits the body when we exhale. There
is a relationship between the amount of alcohol in the blood and the amount in the breath.
2100 mL of air expelled from the lungs contains the same amount of alcohol as 1 mL of
blood.
To determine the amount of alcohol in the breath, the subject breathes into a mouthpiece
that is connected to the sample chamber. The sample is then bubbled through a vial
containing sulfuric acid, potassium dichromate, silver nitrate and water. The purpose
of each substance is
1. The sulfuric acid removes the alcohol from the air so that it dissolves in the water.
Creates an acidic environment needed for the reaction to happen.
2. Potassium dichromate reacts with the alcohol in solution.
3. The silver nitrate acts as a catalyst.
4. Water is a solvent for the other reactants.
A catalyst is a substance that does not participate in a chemical reaction but makes it
easier for the reaction to take place.
The chemical equation for the reaction is given below.
2 K2Cr2O7 + 3 CH3CH2OH + 8 H2SO4 → 2 Cr2(S04)3 + 3 CH3COOH + 11 H2O
Potassium
dichromate
Ethanol
Sulfuric
Acid
Chromium
Sulfate
Acetic acid
Water
Potassium dichromate when dissolved in water is a reddish-orange. After the reaction
has occurred and chromium sulfate is formed, the solution turns green. The degree of the
color change is directly related to the concentration of the alcohol that was present in the
solution.
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Canine Units
Finally an old-fashioned and still very reliable means of detection of materials in luggage
or on persons traveling, and for the detection of accelerants used in arson cases is the dog.
Many airports have K-9 teams that are led through the airports by their law enforcement
handlers (in uniform and plain clothes) sniffing for narcotics, explosives and other
restricted items and materials.
When you have read and reviewed the information in
this module, inform your instructor you are ready to
write the test.
If you have not completed 5 labs, you will need to
complete a forensic report. See your instructor about
this.
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Resources
www.csfs.ca/
Canadian Forensic Society
Web Page
Information on DNA database
in Canada, careers in forensics,
history and online access to
back issues of Canadian
Forensic Journal
home.earthlink.net/~thekeither/Forensic/forsone.htm
Web site explaining many
issues related to Forensic
Science in easy to understand
language and terms
seahorse.louisiana.edu/cmps619
Website providing diagrams of
/Pdf/Lect%202%20Sequences.pdf
DNA and explanations about
the structure
www.biology.washington.edu/fingerprint/dnaintro.html Website explaining one DNA
fingerprinting process.
Ramsland, K. (2001). The Forensic Science of C.S.I.
Book discussing many aspects
New York: Berkley Boulevard Books.
of solving crimes. Case
examples are given.
www.mos.org/sln/SEM/works.html
Provides self-paced and
automated presentation of how
the SEM works.
http://forensics.edu.au/sections.php
Website for the University of
Technology Sydney Centre of
Forensics. Links to many
topics examined in this unit.
www.howstuffworks.com/breathalyzer.htm/printable
Website explaining how the
Breathalyzer works and links to
other related sites.
Exhibit A – The Secrets of Forensic Science
Weekly series on Discovery
channel which looks at the role
forensic science plays in
solving crimes.
www.crimespider.com
Search engine devoted to
finding sites relating to
forensics.
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