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

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

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

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

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

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

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?