Blog Address: https://forensicsciencesubjectivity.wordpress.com/
FORENSIC SCIENCE: SUBJECT TO HUMAN
ERROR
An overview of the scientific processes and subjectivity of four Forensic Science
disciplines.
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By [student name withheld]
F
orensic
Science, or criminalistics,
is a science of comparison
and classification.
It boils down to
taking evidence from a
crime scene and
classifying what it is, then
comparing it to samples or
other evidence until a
match is found. For
example, a bullet is found
at a crime scene. The first
thing determined is its
caliber and the type of gun
it was possibly fired from.
From there, any other guns
that come into the
investigation as evidence
will have the bullets
compared to the one found
in an attempt to find a
match. Forensics and all its
disciplines involve the
combined sciences of
biology, chemistry, and
medicine. The aim of the
forensic scientist to is take
apart, understand, classify,
and compare evidence to
aid investigations. The
final result of which is to
provide proof for
presentation in court to
determine who is the guilty
or non-guilty party by
understanding what may
have occurred. Forensic
scientists may also be
called to testify the validity
of their findings in court.
Although the study
of forensics has existed in
some form or another all
throughout history, it
became a professional
practice in the 1800s with
the three sciences
combining to join law and
criminal justice.
Once the discovery
of the DNA fingerprint
was made many past
convictions were
overturned. The new test
proved many people
previously prosecuted as
innocent and wrongly
convicted due to less than
infallible evidence. DNA
evidence became the new
standard in forensic
science.
Forensic science
involves several different
disciplines, methods, and Alec Jeffreys at work in his University of
tests. DNA fingerprinting, Leicester laboratory, 1985 University of Leicester. Digital image.
Visible Proofs: Forensic Views of the Body. National Library of
friction ridge analysis,
Medicine, 5 June 2014. Web. 1 Dec. 2014.
ballistics, odontology,
<http://www.nlm.nih.gov/visibleproofs/galleries/cases/jeffreys.html>.
forensic psychology,
DNA
forensic etymology,
forensic accounting, hair
he DNA fingerprint
fiber analysis, toxicology,
was discovered by
and more are all different
Professor Sir Alec Jeffreys
disciplines under
on September 10th, 1984.
criminalistics.
In 1977, the molecular
biologist came to the
T
University of Leicester
searching for variations in
the human DNA sequence.
While working on a project
concerning the structure of
the gene responsible for
encoding protein
myoglobin Jeffreys
obtained seal meat for
testing from the British
Antarctic Survey office
because seals produce
more of the myoglobin
than humans. From there
he moved onto humans and
discovered the repeating
DNA segment.
This lead to the
discovery that portions of
the repeating section were
similar to others found in
STR regions, suggesting
similarity to STR regions
in DNA. Using several
people’s DNA and a
molecular probe he
investigated if these
regions varied person to
person.
––––––––––––––––––––––
As Jim Fisher states
in his book
Forensics Under
Fire, “As of 2007,
190 prisoners
nationwide have
been exonerated
from DNA testing.”
––––––––––––––
Jeffreys described
his discovery as a “Eureka
moment.” (“Forensic
Tools”) A discovery that
would soon be put to the
test. Within two years of
his discovery DNA
fingerprinting would be
used to exonerate an
innocent juvenile in a
murder investigation and
be applied on a wide scale
to discover and convict the
real culprit.
DNA determines
the development of an
individual and their traits.
Two percent of DNA is
responsible for features
such as eye, hair, and skin
color. This is called the
coding region. The
remaining 98%, also called
the non-coding region, is
used by forensic scientists
in criminal investigations.
It is in this 98% that
contains a pattern unique
to each individual. DNA
evidence can be found in
blood, hair, saliva, semen,
urine, bone, tissue, and
more. These can be found
at a crime scene or items
within a crime scene such
as a weapon, clothing, or
anything touched by any
involved parties.
In investigations
this evidence goes through
several stages. Initially, the
collected evidence is sent
to a DNA analyst for
testing. From there the
DNA is extracted from the
cell. Then it goes through
quantitation, which
determines how much
DNA is in the sample.
Next the amount of DNA
is amplified to multiple the
copies of DNA to allow for
characterization. The DNA
is then separated to allow
for identification. From
there the sample is
analyzed and the result
interpreted. This includes
submitting DNA profile
into the local, state, or
national databases of
collected DNA samples to
search for a match or being
compared to other
collected samples from the
scene and suspect samples.
It must also go through a
quality assurance, a review
of the results for accuracy.
DNA evidence has
many uses. It can link a
criminal to a victim,
identify a victim or
remains, identify family, or
rule out suspects. DNA is
not used in all types of
criminal investigations.
Because of limited
resources it is usually
reserved for sexual
assaults, homicides,
robberies, and missing
person cases.
The case where
DNA profiling in the
conviction of a criminal
was first used was in the
rape and murder of two
girls. Although the
murders were three years
apart there were enough
similarities for the
investigators to treat them
as linked cases with the
same culprit. Although
there was a suspect, a
young man named George
Howard, and a confession
to one of the murders the
investigators had no other
serious evidence with
which to get a clear
conviction. As such
Jefferys was asked to
perform a DNA test to
compare Howard’s blood
to fluids on the two victims
clothing. The results
cleared Howard as a
suspect and revealed a
false confession making
George Howard the first
man to be exonerated with
DNA evidence.
At the time of this
investigation, with DNA
fingerprinting being at an
infant stage, no database
existed with DNA profiles
to compare the killers
sample to and thus the
investigation reached a
standstill. To overcome
this problem the police
collected DNA samples
from all men in the area of
the murders for
comparison. After
collecting over 4,000
samples without a match a
break in the case was
made. It was realized that
with the means to
positively identify the
culprit with their DNA, the
culprit would not be
inclined to willingly give
the police a sample and the
means to convict him.
Luckily, shortly after this
realization a group of
people inside a pub
overheard a man say that
he had given his blood for
someone else. This
someone else was Colin
Pitchfork. Pitchfork was
found and a sample was
taken that was a positive
match to the DNA on the
victims. This lead to the
conviction of Pitchfork for
two life terms in prison,
making him the first man
to be convicted with DNA
evidence.
Although
uniqueness of DNA is
what lends to its value in
criminal investigations it
does come with
drawbacks. For instance,
when DNA evidence is
unsuitable for use. If a
sample taken contains low
quantities of DNA, or its
quality has degraded due to
environmental conditions
or improper preservation,
the result will be a partial
profile. While a partial
profile may be used to
include or exclude
individuals from an
investigation, each DNA
database has minimum
qualifications before it can
be submitted which would
render the sample
unsuitable for submission.
Human error also
plays a role, as it does with
all forensic disciplines.
DNA tests are susceptible
to false positives,
contamination, mistakes in
gathering and testing, or an
incorrect interpretation.
Despite these
drawbacks, the
introduction of DNA
analysis in criminal
investigation has had an
unprecedented impact on
crime. The presence and
location of DNA on the
scene can prove or
disprove the location of a
crimes occurrence and
prove or disprove a
suspects alibi. Since its
discovery and application
cold cases have been
reopened to investigation
with a new way to test
evidence and closed cases
reopened to contest
convictions based on other
evidence. The result has
been the freeing of many
innocent people wrongly
convicted. As Jim Fisher
states in his book Forensics
Under Fire, “As of 2007,
190 prisoners nationwide
have been exonerated from
DNA testing.” (231)
Fingerprints
In 1877 Thomas Taylor
suggested the markings on
palms and fingertips could
be used for identification
in criminal cases. In 1880,
Scotland’s own Henry
Faulds published a paper
on the possibility of
identifying criminals with
fingerprints at the scene of
the crime-then used it to
find the culprit in burglary
case in Tokyo. Fingerprints
had been in use for
identification, business
transactions, forgery
prevention, and more for
hundreds of years before
its application to crime.
In 1910 the case of
The People v. Jennings
was the first to admit
fingerprint evidence. After
breaking into the home of
Mary Miller, murdering
her husband, and violating
her daughter Thomas
Jennings was stopped by
the police a mile from the
scene and arrested. With
fire arm identification not
yet possible there was no
way to place Jennings at
the scene after a distraught
Mary was unable to
identify the burglar in a
police lineup. However, a
detective discovered four
fingerprint impressions on
the freshly painted porch
rail outside the window the
intruder entered through.
Jennings prints were
identified as a match by
three experts at the trial.
Jennings attorney objected
to the use of evidence on
the grounds that friction
ridge analysis had not yet
been scientifically tested in
its reliability and was
unreliable. The judge
overruled this objection
and Jennings was found
guilty. From that point on
fingerprint evidence would
be admitted in every court
under high authority, until
the discovery of the DNA
fingerprint which would
change the field of forensic
science.
Fingerprints can be
left behind on solid
surfaces and objects,
including skin, although
they are more easily
collected from smooth
surfaces. Fingerprints are
classified into three
categories: plastic, patent,
and latent. Plastic prints
are those left on soft
surfaces such as soap.
Patent prints are those left
when a finger or hand
covered in a substance,
such as blood, transfers the
substance onto another
surface. For example, a
bloody fingerprint on a
doorway. Latent prints are
left behind by natural body
oils onto the surface they
touch and are invisible to
the naked eye. These prints
can be revealed through
use of a special light
source, exposure to certain
chemicals, or through a
process called
Cyanoacrylate fuming.
With this the object the
analyst is trying to lift the
print from is enclosed in a
machine and exposed to
the fumes of heated
superglue which adheres to
the oils left behind by the
skin onto the object and
reveals the print.
When a fingerprint
is lifted it is because the
chemicals exposed adhered
to the frictions ridges and
furrows of the finger, that
is, the raised and recessed
ridges on the skin that
create the pattern on the
finger. Fingerprints are
classified into three
different groups:
loops, whorls,
and arches. A
loop pattern is
one that curves
back into itself.
Whorls form
circular patterns.
Arches are a
wave type
pattern created
by rising and
dipping of the
arches.
Friction
Ridge Analysis is
done by forensic
scientists,
technicians, or
police officers
with the
Fingerprint Patterns:
correct
Loops, Whorls, and
qualifications Arches. Digital image. Forensic
in a crime lab Science Simplified. National Forensic
Science Technology Center, n.d. Web.
or law
1 Dec. 2014.
enforcement
<http://www.forensicsciencesimplifie
agency. If the d.org/prints/principles.html>.
criminal case
is high profile or if there is
another need the analysis
may be done by private
companies. Fingerprints
are taken from crime
scenes and compared to
victim, witness, and
suspect prints. After they
are collected they go
through the Analysis
Comparison Evaluation
and Validation or ACE-V
method. During the
analysis the collected print
is analyzed to determine if
it is suitable for
comparison. A print may
be determined unsuitable
due to the quality of the
print which could be
affected by factors such as
weather exposure or poor
handling when collected. If
it is determined unsuitable
the process goes no
further. If it is determined
suitable the print is
analyzed for any features
that may aid comparison,
such as scars. During
comparison, the collected
prints are compared to
known prints to determine
a match. Known prints are
those collected during the
investigation from persons
of interests as well as those
catalogued in fingerprint
databases such as the FBI’s
Integrated Automated
Fingerprint Identification
System or IAFIS, the
largest collection of
fingerprints in the world.
The evaluation step is
when the analyst
determines if the collected
print and the known print
are a match, not a match,
or if the results are
inconclusive. For quality
control purposes the entire
process is redone by a
different analyst to either
validate or refute the
original conclusions.
This largest
attraction of friction ridge
analysis is on the
uniqueness of every finger
and thumb print between
individuals. No two
people, even twins, will
have the same markings.
Although damage can
occur to the ridges from a
trauma the skin will remain
with the same pattern when
it heals. Although there
can be cases where the
damage is so severe the
print is altered but the
result will be a new print
pattern which will also be
unique.
While fingerprints
are useful in investigations
when DNA evidence is
unavailable there are
drawbacks. As with DNA,
without a sample for
comparison it will not be
useful past determining
individuals who are not a
match until such time as a
possible match is
discovered. However, the
bigger issue concerning
this field as is with many
others is the subjectivity of
the interpretation of the
evidence.
In 1997 fifty-one
year old Marion Ross was
found dead from stab
wounds in her bathroom.
David Asbury, a
construction worker from
the area was named a
suspect. No prints of his
were found in the victim’s
home but the victims
fingerprint were found on a
tin in Asbury’s home with
a large amount of money
which he claimed was his.
This print was lifted by
thirty-four year old
detective constable Shirley
McKie.
Her celebration
over finding this key piece
of evidence was shortlived. A bloody left
thumbprint had been found
on the bathroom doorframe
was identified as her own
by the Scottish Criminal
Records Office (SCRO).
However, McKie claimed
to never going past the
front porch into the
victim’s residence and that
the print was not hers.
Fingerprint
evidence was at this point
considered absolutely
infallible and her denial of
the print belonging to her
made her look like a liar.
No one believed her and
her job was at risk, she was
even begged by several of
her coworkers to confess to
no avail. While McKie was
questioned on stand about
her print in an attempt to
call to question the
evidence she maintained
her innocence and Asbery
was convicted for the
murder.
McKie was arrested
in 1998 for committing
perjury. After making bail
and being suspended from
duty pending her trial
McKie sought out Patrick
A. Wertheim, an expert
analyst with 20 years of
experience among other
qualifications. He agreed
to compare the print found
to McKie’s and discovered
that they did not in fact,
match. He was joined by
Illinois State Crime Labe
fingerprint examiner David
L Griece and New
Scotland Yard’s Allen
Bayle, the United
Kingdom’s foremost
expert in fingerprint
analysis to testify on
McKie’s behalf in court.
The four SCRO
responsible for the
identification, who were
also on suspension,
maintained their analysis
of the print.
After eight years
and multiple trials McKie
was able to settle out of
court, but without her
career and friction ridge
analysis suffered a drag
through the mud. During
those eight years,
numerous experts were
called to testify, the SCRO
were accused of altering
the evidence to cover a
false identification, and the
FBI were accused of trying
to sway the results as the
effects of a blow to the
validity of the science
would have affected an
entirely different case.
While the eyes of
the scientific world were
on Shirley McKie and the
SCRO, the original case of
the murder of Marion Ross
was solved when the real
culprit was identified and
Bullet Comparison. Digital image.
Forensic Science Simplified. National Forensic
Science Technology Center, n.d. Web. 1 Dec. 2014.
<http://www.forensicsciencesimplified.org/firearms
/principles.html>.
arrested, but not before the
mistake cost the life of
another woman. With the
addition of McKie out of
the job and the SCRO
shamed, the reputation of
the friction ride analysis
science did not come away
unscathed.
Bullets
The first use of bullet
comparison to catch a
criminal was in 1835 when
Henry Goddard of
Scotland Yard traced a
bullet to a mold with flaw
in the bullet. Since then the
techniques of comparison
and the technology to
utilize this branch of
investigation grown into
worldwide use in
convicting criminals.
Ballistics is the
branch of forensics
focusing on firearm
identification. The aim of
ballistics is to use a
cartridge case, the
container for the cartridge
which is an unfired bullet,
primer, and smokeless
powder, or fired bullets, or
bullet fragments found at a
crime scene to find the
weapon it came from.
When a bullet is fired it
becomes marked by the
inside of the gun which
leaves microscopic
markings on the bullets
surface matching those
characteristics. No two
guns characteristics are the
same, including those of
the same gun model. If a
bullet or casing is found at
a crime scene an analyst
can document those
features and later compare
them to other bullets with
the use of a comparison
microscope.
There are several
characteristics that can be
used to classify a bullet or
casing. The caliber, or
diameter of the guns barrel
and the grooved
impressions, the interior of
a guns barrel that is cut to
form a rifling pattern
which is used to create a
spin on the bullet once
fired to increase accuracy
as well as individual
characteristics such as
imperfections or damage
are used as points of
comparison. After the
bullets have been
measured and weighed a
stereo microscope is used
to determine class
characteristics and the
comparison microscope is
used to compare the bullet,
fragment, or casing
collected for comparison.
To safely collect a bullet,
labs need a way to fire the
gun and collect the bullet,
a common is the use of the
water recovery method.
This involves using large
tank of water to discharge
the gun and collect the
bullet.
As with DNA and
Friction Ridge analysis,
without something to
compare the bullet or
casing to, an analysis can
only be useful as far as
classifying the evidence
until a time there is one
available for comparison.
Another is the condition of
the evidence upon
collection. If the bullet or
cartridge is too damaged
from impact, use, age,
weather conditions, etc.,
the individual
characteristics will be too
difficult to distinguish.
After all tests have
been completed the
examiner can make one of
four possible conclusions,
the bullet or cartridge was
discharge from the
collected firearm, it was
not discharged by the
collected firearm, there
were insufficient
characteristics to properly
give a conclusion, or it was
not suitable for
comparison. However,
there was a time when a
court accepted method
existed for identifying
damaged bullets.
In an attempt to link
Brown to the crime
the prosecution
hired Dr. Edward
Mofson, a local
dentist with no
forensic training.
––––––––––––––––––––––
When a new
method for analyzing
evidence is discovered, the
technology, processes, and
all other relevant
information makes its
round through the
scientific community.
However, this was not the
case with comparative
bullet lead analysis or
CBLA. This process of
matching bullet fragments
to unfired ammunition was
purely an FBI process. The
focus of CBLA was the
identification of fragments
from bullets too damaged
for standard comparison by
matching them to
ammunition in the
suspect’s possession. This
process assisted in 2,500
cases with no question on
its validity. This evidence
was difficult to refute in
court due to all experts in
the process being FBI. It
wasn’t until the case of
Michaels Behn that it was
challenged. Behn was
accused of shooting a coin
dealer. He was linked to
the crime by various
evidence which would
ultimately have him
convicted after two trials,
the first with the CBLA
evidence and the second
without.
After being
convicted in the first trial a
former FBI chief
metallurgist, who deals
with the study of metals,
took an interest in the case
after being contacted by
Behn’s sister for help with
the case. CBLA was based
on the each batch of lead,
which would later be
formed into bullets, is
consistent in its chemical
composition and that each
batch had its own unique
composition. Tobin’s
research into CBLA lead to
the conclusion that the
composition of lead
batches is not necessarily
unique, that bullets within
the same batch were not
always a match in their
composition, and that
although Behn’s
ammunition and the crime
scene bullet were shown to
have been created on the
same day, they were not
necessarily from the same
batch as multiple batches
can be created in a single
day but they are not
necessarily distributed at
the same time. The end
result of this and additional
analysis led to the
recanting of the process
and forced a reevaluation
on all cases whose
outcome were affected by
the now debunked
evidence.
Human
interpretation will
always have the
largest impact on
the science,
regardless of how
advanced the
procedures are for
any particular
discipline.
––––––––––––––––
Although the
validity of CBLA was
called into question there
have been no such issues
concerning the current
method of comparison
beyond the fact that it, just
like Friction Ridge
Analysis, is subjective and
its effectiveness is
dependent upon those who
conduct and analyze the
findings.
Teeth
The first American
Odontologist was Paul
Revere who used his skills
as a dentist to identify Dr.
Joseph Warren by the
silver and ivory bridge in
his teeth. Forensic
Odontology is often used
in non-criminal related
cases, for identification of
remains and unidentified
bodies during disasters.
However, it is also a tool
for court room evidence.
Odontology is the
use of dentistry in forensic
to identify a criminal
though bite marks left at
the scene. Bite marks may
be found in food or the
victim. Although
odontology is useful for
the identification of
remains here the focus will
be in crime. Once a bite
mark is discovered it, as
with other evidence, is first
photographed. From there
a swab is used to take a
is made, can be used for
comparison. Another such
technique is the use of
transparent overlays. This
involves a drawing of teeth
edges of the evidence and
suspects, done on
transparent acetate paper,
and laying the images atop
each other to make any
differences visible.
One large issue
with this dental form of
identification, particularly
when analyzing marks left
in flesh is how easily the
markings can be altered.
Skin is elastic and
therefore susceptible to
stretching, and if the body
or part which contains the
mark is moved or there are
changes in the weather
condition, the original
impression can be
damaged or changed.
In 1991 Roy A.
Brown was accused of
arson and murder. His
only link to the crime,
was a bite mark found
on the victim. In an
attempt to link Brown
to the crime the
prosecution hired Dr.
Edward Mofson, a local
Bite-mark Comparison in State v. Krone, 182 dentist with no forensic
Ariz 319. 1995. Ourt, Challenges in the Twenty-First
training. Mofson
Century. By Donald Shelton. N.p.: Rowman &
identified one of the
Littlefield, 2010. 74. Print.
wounds, left by six upper
saliva sample to obtain
teeth, on the victim to
DNA for analysis. A mold
Brown. His analysis was
or cast of the impression
called into question by the
can then be made. If
defenses expert forensic
another bite mark is found,
dentist, Dr. Homer
or if a mold from a suspect
Campbell, who countered
with the question of how a
match was possible when
his defendant was missing
two of his upper front
teeth. Mofson argued that
the wound could have
possibly twisted in a
manner which made the
impression appear filled,
although none of the other
marks were identified.
Despite the glaring
problem with the evidence
and prosecutions expert
witness the jury found the
defendant guilty and he
was sentenced to 25 years
in prison. However, after
15 years he was exonerated
without an additional trial
when new DNA evidence
linked another man to the
crime, one would kill
himself before standing
trial.
Despite the glaring
drawback subjectivity can
have on science of any
nature, odontology
continues to thrive with
along with many others, its
theory, testing, and
application widely
accepted as a valid science
in the courtroom with the
idea that teeth, like
fingerprints, DNA, and
bullets have the
characteristics of
uniqueness for support in
their validity.
DNA, friction
ridge analysis, ballistics,
and odontology are only a
few of the many different
methods used in criminal
instigations. With the aim
to find, classify, compare,
and match evidence until
the crime scene becomes
clear. Comparison and
classification is key to
these and all others types
of forensic science. As
such the biggest difficulty
facing forensic science is
its subjectivity to human
opinion. Human
interpretation will always
have the largest impact on
the science, regardless of
how advanced the
procedures are for any
Sources Consulted
particular discipline.
Professionals must strive
to remain so and be weary
of the unprofessional
opinion when findings in
criminal investigation are
inevitably placed under
scrutiny.
Despite all
difficulties forensic science
is instrumental in crime
scene investigation, taking
a crime scene and
recreating what happened,
connecting the pieces, and
aiding in clearing innocent
people and identifying true
culprits.
Forensic science
has existed in some form
all through history,
evolving overtime as
various different
disciplines all intertwined
in their dependence on
interpretation. As
technology and
understanding of the
science grow, forensic
science can only improve.
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