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Forensic Science
Unit D: Summary
Forensic Engineering

Concerned with:
– Failure analysis
– Accident reconstruction
– Cause and origin of fires or explosions

Answer questions such as how did an
accident occur or what structural failure
occurred
Forensic Pathology

Involves the investigation of sudden,
unnatural, unexplained, or violent deaths.
– Typically these are the medical examiners or
coroners

Answer questions: who is the victim, what
injuries are present, when did the injuries
occur, why and how were the injuries
produced, and what is the cause of death
Criminalist (CSI)
Analyzes, compares, identifies, & interprets
physical evidence at crime scenes.
Forensic Anthropology

Identification and examination of human
skeletal remains
– Trying to determine origin, sex, approximate
age, race and skeletal injury
– May create facial reconstruction
– Identify victims of mass disaster such as plane
crash
Forensic Toxicologist
Analyses alcohol, drugs, & poisons in body
fluids for the benefit of the courts.
Manner of Death
Natural:
 Homicide
 Suicide
 Accidental
 Undetermined

Cause of Death

Asphyxiation
– Strangulation
– Drowning
– Fire victim

Exsanguination
– Major blood loss
Blunt force trauma
 Sharp force trauma
 Chemical trauma

Estimated Time of Death
Autopsy
 Rigor Mortis: the stiffening of body parts in
the position they are in when death occurs.
 Lividity: medical condition that occurs after
death and results in the settling of blood in
areas of the body closest to the ground
 Body Temp: postmortem changes that
cause a body to lose heat. 1-1.5o C/hr

Estimated Time of Death
Livor Mortis or lividity: medical condition
that occurs after death and results in the
settling of blood in areas of the body
closest to the ground. Begins immediately
after death and lasts for 12 hours
 Algor Mortis: postmortem changes that
cause a body to lose heat. Process in
which the body continues to cool to room
temperature. 1 – 1.5 degree/hour

Forensic Entomology

Study of insects and
their relation to a
criminal investigation

After decomposition
begins, insects such
as blow flies are the
first to infest the body
Arriving at the Crime Scene
Secure and isolate the crime scene
 Determine boundaries of crime scene and
priorities for evidence collection
 Rough sketch
 Finished sketch
 Photograph
 Videotaping
 Notes

Collecting Evidence
Conduct a systematic search for evidence;
be unabiased and thorough.
 Field technicians
 What to look for depends on the crime
and what specific locations of the crime
scene would most likely be affected
 Microscopic or massive objects
 Collect carriers of possible evidence
 Vacuum or sweeping collected

Packaging of Evidence
Prevent any changes from occurring
(contamination, breakage, evaporation,
bending, loss)
 Process trace evidence from original object
(shirt, shoe) rather than isolating and
packaging if possible
 Package evidence separately

Chain of custody
Continuity of possession; every person
who touched it must be accounted for
 Standards for collecting, labeling, and
submitting evidence forms are necessary
for court
 Labels include collectors initials, location
of evidence, date of collection.
Identification numbers must also be used

Submission of Evidence
Standard/reference samples
 Substance controls
 Evidence submission form will detail the
evidence collect and particular type of
examination/analysis requested.
 Lab tech not bound by requests

Methods of Detection

Types of prints
– Latent print
– Visible print – deposited ink, blood, dirt
– Plastic print – impression in a soft surface
Most natural finger prints consists of
secretions of the skin’s glands
 Developed by either powders or chemicals

Fingerprints

History
– Japanese used thumb print as a signature
on documents until 1860.
– First used in crime in 1901 by Sir Edward
Richard Henry

3 Patterns
– Whorl
– Loop
– Arch
Categories of Fingerprints
Loop – ridge lines enter one side of
pattern and curve around to exit from the
same side of pattern. (65%)
 Whorl – ridge lines rounded or circular and
have two deltas(30-35%)
 Arch – ridge lines enter print from one
side and exit from the other (5%)

Blood Evidence
Serology: the study of antigen – antibody
reactions using laboratory tests
 Kastle-Myer Test – Is it blood?
 Precipitin Test – Is it human blood?
 DNA Analysis – Whose blood is it?

ABO blood typing
RBCs have A, B, neither, or both antigens in its surface. Serum
carries antibodies against antigens it does not have. O negative
carries no Ag and therefore does not react with any Anti A, B, AB. Rh
factor is a separate protein on the surface of RBCs
Pos reaction
Neg reaction
Blood Splatter Analysis
Location, distribution, and appearance of
blood stains are an important part of
forensics
 Investigators try to determine:

– Direction
– Dropping distance
– Angle of impact

Splatter analysis is often used for crime
scene reconstruction
Blood Splatter Analysis

Factors which influence stain patterns are:
– Surface texture
– Direction of travel
 Pointed end of bloodstain always faces its direction
of travel
– Angle of impact is determined by measuring
the degree of circular distortion of the stain
 Blood striking a surface at right angles gives rise to
a nearly circular stain
 As the angle decreases, the stain becomes
elongated in shape