1. Types of evidence “Forensic Scientists are not policemen.
We are scientists.
We deal with these matters objectively.
We do not act on our suspicion”
- Cycil Wecht

2. Locard’s Exchange Principle
“The exchange of materials between two objects that occurs when those two objects come into contact with one another”
Edmond Locard strongly believed that every criminal can be connected to a crime by dust particles carried from the scene.
EVERY Criminal either leaves behind a piece of himself (or herself), carries a piece of the crime with him (or her), or both
In other words, there is always evidence to be found.
All Evidence is generally classified as either testimonial or physical evidence

3. Testimonial Evidence
What is said in court by a competent witness under oath
Also known as direct evidence or prima facie evidence
The key word here is competent
Many factors can affect the accuracy of testimony

4. Factors affecting memory of witnesses
Positive factors
Negative factors
Environmental conditions
Dark, foggy, etc.
More specific characteristics
Age, height & race
Leading questioning
Power of suggestion can actually change a memory
Stress & Fear
For some, it clouds the mind
Intoxication
Drugs and drinking are bad for you
Type of witness
Children and the elderly are usually less reliable; as are others
Suspect closely resembles the witness
General characteristics
Sex & hair color
Stress & Fear
Stress often sharpens the mind
Victims of serious crimes
These relive the experience

5. Physical Evidence Tangible items that tend to prove some material fact
This is what forensic scientists are most concerned with (and comprises more than ¾ of this course)
Tangible items that tend to prove some material fact
Also known as Real Evidence
Most evidence does not prove a fact and is therefore referred to as INDIRECT EVIDENCE
Some evidence does
possession of…
Blood alcohol content

6. Physical Evidence
Circumstantial evidence- evidence based on suggestion that implies a fact or event without actually proving it.
Probability & Statistics come into play. How likely is this evidence related to the perpetrator
The more Circumstantial evidence you have, the greater the weight it carries.
Individual evidence- Material that can be related to a single source
individualization involves comparison
Class Evidence- Material that can be related to a group of items that share similar characteristics
Probative value- The evidence’s ability to prove something

7. Scenario A stabbing occurs resulting in death.
Method of entry & exit is through a broken east facing window
A suspect is found near the scene. He is in possession of a pocket knife with red residue on the blade. He also has red fluid stains on his person and clothing.
There are glass shards in the treads of the suspect’s shoes
For your Reflective Journal, answer the following…
What circumstantial evidence can you immediately identify?
What other evidence might you look for?
How could you increase the probative value of each piece of evidence?