Transcript to Intro Forensic Science

Locard Exchange Principle
It was the French scientist Edmond Locard, a
pioneer in forensic science, who declared (in
French) that "it is impossible for a criminal to
act, especially considering the intensity of a
crime, without leaving traces of his
presence."
"Every contact leaves a trace."
Four Main Elements to an
Investigation
First, the crime scene is thoroughly
documented. Photographs, videos, sketches
and notes describing the scene are made.
Second, the physical evidence is collected
and unknown substances are sent to the
laboratory for identification and analysis.
Four Main Elements to an
Investigation
Third, the results of the laboratory analysis
of the physical evidence are compared to
witness statements.
Finally, both witness statements and
laboratory results are used to disprove the
investigator's hypotheses until one
remains.
Bertillon in 1883
Anthropometrics
literally meaning "measurement of
humans"), refers to the measurement of
living human individuals for the purposes
of understanding human physical
variation.
From these studies, it was discovered
that ratios existed between various
body parts and the height of the
person.
Comparison Microscope
Goddard in 1925
Ballistics: the study of the motion
of bullets and their examination
for distinctive characteristics after
being fired. Examiners can use
this evidence to match bullets or
bullet fragments to specific
weapons.
Blood Typing
Karl Landsteiner in 1901
Blood type:
Antigens on red cells:
Antibodies in serum:
A
A
Anti-B
B
B
Anti-A
AB
AB
Neither anti-A or anti-B
O
Neither A nor B
Both anti-A and anti-B
O
A
B
AB
43-45%
40-42%
10-12%
3-5%
O+ 39%
O- 6%
A+ 35%
A- 5%
B+ 8%
B- 2%
AB+ 4%
AB- 1%
Large spots - the blood was travelling at a relatively
low velocity
Small spots - the blood was travelling at a relatively
high velocity. (More force equals smaller splatter)
Elongated drops - victim was moving, their speed
relative to the amount the spots are stretched and how far
they are spaced apart. (Also indicates directionality)
Void in otherwise uniform splatter - something blocked the
blood spray.
Contact - large stain on a surface caused by contact with a
bloody object.
Cast-off - straight, elongated lines of splatter indicating
that blood was thrown by a moving object in a change of
direction. (Can show how many times a victim was struck)
video
DNA
This provides a powerful technique for
uniquely identifying the person or animal
who left traces of body fluids at a crime
scene. Indeed, this is the best method
presently known for such identification.
DNA Electrophoresis: the process that
separates DNA using gel and
electricity
DNA Profiling: the process of testing to
identify DNA patterns or types
TOXICOLOGY
Toxicology: the study of
poisons and drugs and their
effect on human and animal
populations.
Gas Chromatograph (GC): a forensic tool used to
identify the chemical makeup of substances used
in the commission of crimes. The questioned
substance is burned at high temperatures. The
temperature at which this material becomes gas is
then charted to determine its makeup.
Forensic Odontology
Bite mark comparison is fairly new, however, going back to the mid-1970s.
Criminals seem to leave their bite impressions on food products, chewing
gum, or more commonly on the skin of their victims
There are seven (7) types of bite marks
1. hemorrhage -- small bleeding spot
2. abrasion -- undamaging mark on skin
3. contusion -- ruptured blood vessel, bruise
4. laceration -- punctured or torn skin
5. incision -- neat puncture of skin
6. avulsion -- removal of skin
7. artifact -- bitten-off piece of body
Fingerprints
• Sir Francis Galton in 1888,published his
book, "Fingerprints", establishing the
individuality and permanence of
fingerprints. The book included the first
classification system for fingerprints.
Whorl 30%
Arch 4%
Loop 65%
Solve the crime