1. Forensic Science Criminalistics Chapter 2 and Chapter 3
The Crime Scene and Physical Evidence

2. Goal of any crime scene investigation….
Recognize, document and collect evidence at the scene of crime.
This should lead to a conclusion of some sort- an arrest of a suspect, determination of motive, etc.

3. Principle of Exchange
Whenever two people or things come into contact with each other, a physical transfer occurs.
Trace evidence: transferred materials left at a crime scene.
Locard’s Principle

4. Physical Evidence: any object or material that is relevant in a crime.
Should provide a link between a crime and the victim or perpetrator.
Ex. Hair, fibers, piece of crashed automobile, etc.

5. What is evidence?
Direct Evidence: Evidence in the form of a statement and made under oath.
Ex. Eyewitness testimony. (Pointing to the defendant in the courtroom and saying, “He did it!”)
Police car dash cameras

6. Common Types of Evidence:
Drugs and toxic substances
Soil, glass
Paints
Blood
Gunshot residues
Body fluids
Firearms and ammunition
Fingerprints
Impressions (shoe prints, bite marks, etc)
Hair
Tissues
Petroleum products
Pollen
Alcohols
Wood materials
Rubber material
Feathers
Resins, plastics
Bones
Explosive residues
Documents
Fibers

7. If evidence does not prove a fact it is called indirect evidence.
Circumstantial evidence implies a fact or event. The greater the volume of circumstantial evidence there is, the greater weight it carries.

8. So, what good is evidence?
Physical Evidence should be able to:
Prove that a crime has been committed
Corroborate testimony
Link a suspect with a victim or with a crime scene
Establish the identity of persons associated with a crime
Allow reconstruction of events of a crime

9. Rules of Evidence
Must be relevant which means it must prove something, and must address the particular crime.
Evidence is admissible only if it is reliable and the presenter of evidence is credible and competent.

10. The scientific theory or technique must be testable
While we know that using the Frye Standard, testimony and scientific procedures must be “generally accepted”, here are some guidelines for judgement:
The scientific theory or technique must be testable
The theory or technique must be subject to peer review and publication.
Rate of error or potential errors must be stated.
The technique must follow standards.
Consideration must be given as to whether the theory or technique has attracted widespread acceptance within a relevant scientific community.

11. Individual vs. Class Evidence
Individual Evidence:
Evidence that can be associated with a common source with a high degree of probability
Examples:
Matching ridge characteristics of two fingerprints
Matching striations on bullets
Matching irregular and random wear patterns on footwear

12. Class Evidence: Examples:
Properties of evidence that can only be associated with a group and never with a single source
Examples:
Brands of items or manufacturers.

13. Problems or Exceptions?
Disappointments when the lab is unable to find an exact match.
Weakness
Mostly forensic scientist must rely on personal experience to interpret significance of comparison

14. Recognition: Must recognize that an item is evidence of a crime.
Must be able to separate those pieces with evidentiary value from unrelated materials.

15. Identification Identify class characteristics.
Ex. Determine if hair is animal or human, brown or blond, etc.

16. Comparison
Characteristics of evidence must be compared to a known sample.
Ex. Strand of hair found at a crime scene and you take a strand of hair from a suspect. The hair from the suspect is the known sample for comparison purposes.

17. Individualization Can be matched to a unique source.
Ex. Striation on a bullet can be matched to the firearm.

18. Reconstruction Team event Reconstruct events that occurred
Prior to crime
During crime
Subsequent to crime
Collaborative effort including
Law enforcement, criminalist, Medical examiners

19. The Crime Scene Investigation Team
Police officers: first to arrive
A District Attorney may accompany to determine if a search warrant is needed

20. Crime-scene Investigators
Document scene in detail and collect physical evidence

21. Medical Examiners Also known as a coroner
Determine the cause of death in the case of a homicide

22. Detectives
Look for leads by interviewing witnesses and talking to crime scene investigators about the evidence.

23. Specialists Experts in a particular field pertaining to the evidence
Ex. Botanist, entomologist, anthropologist.

24. 1. Securing the crime scene
Duties of the Arriving Officer:
Get medical attention for suspect or victim
Arrest perpetrator if remaining on premises
Secure the Crime Scene

25. Securing and Isolating a Crime Scene
The Arriving Officer must prevent unauthorized or unneeded access:
Neighbors/Onlookers
Members of the Media
Every individual entering a crime scene can potentially destroy important evidence

26. 2. Separating the witnesses
Want to compare the accounts of each witness
Don’t want them to work together to create a story

27. 3. Scanning the crime scene
Need to determine the primary crime scene and a possible secondary crime scene.
Primary crime scene: where the crime occurred
Secondary crime scene: suspects house, where the body was found, etc.

28. The Lead Investigator will:
Determine the boundaries of the scene
Document and photograph obvious evidence
Develop a strategy for a systematic examination and documentation of entire scene

29. 4. Seeing the scene Methods of crime scene recording Photography
Videography

30. Crime Scene Photography
The crime scene must be unaltered and in the original state found by investigators
Must be photographed from all necessary angles
Evidence must not be moved prior to photography: if it has been moved, it cannot be reintroduced into the scene for photo purposes

31. Crime Scene Photography
Photos must be taken of the entire room and all rooms adjacent to initial crime scene
Close-up photos and panoramic photos are taken and sometimes include a ruler for scale
All pieces of physical evidence are photographed prior to removal

32. Crime Scene Videography
Increasingly popular due to affordable cost
Long-shots and close-ups are taken of scene
Narrations are often included as a method of note-taking

33. 5. Sketching the scene Rough Sketch:
An accurate depiction of dimensions of the scene, showing the location of all objects that may have implications to the crime.
Done at the scene and used for finished sketch later

35. Rough Sketches
Objects are depicted from two fixed locations at the scene
Accurate measurements must be taken with a tape measure
Sketch evidence by using letters or numbers and a legend at the bottom
Sketch should always depict the NORTH direction

36. Finished Sketch A precise depiction of the crime scene, drawn to scale
Sometimes drawn with the aid of a computer
CAD: Computer-aided drafting

37. Notetaking at a Crime Scene
Constant activity at a crime scene that includes the following:
A written description of the scene in a narrative format
Location of physical evidence items recovered
Time evidence discovered and by whom
The condition of the evidence recovered