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

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.

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

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.

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

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

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.

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

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.

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.

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

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.

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

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

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

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.

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

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

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

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

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

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

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

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

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

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

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.

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

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

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

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

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

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

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

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

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