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.

Anthropometrics

Bertillon in 1883

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 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%

Karl Landsteiner in 1901

Blood Typing

video

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)

Contact - large stain on a surface caused by contact with a bloody object.

Void in otherwise uniform splatter - something blocked the blood spray.

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)

DNAThis 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

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.

TOXICOLOGYToxicology: the study of poisons and drugs and their effect on human and animal populations.

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.

Arch 4%

Whorl 30%

Loop 65%

Solve the crime