Forensics Unit 2 Part 1 Notes

Crime Scene Investigation

• Evidence & Crime Scene Investigation
  • The goal of crime scene investigation is to recognize, document, and collect evidence at the scene of a crime. Solving the crime will depend on piecing together the evidence to form a picture of what happened at the crime scene.
• The Locard Exchange
  • Whenever 2 objects come in contact with one another, a cross-transfer of physical evidence can occur.
  • The intensity, duration, and nature of the materials in contact determine the extent of the transfer.
  • Dr. Edmond Locard: Every criminal can be connected to a crime by small particles carried from the scene. 
• Evidence Types
  • Direct Evidence: first hand observation (eyewitness account, videos, confessions)
  • Circumstantial Evidence: indirect evidence that can be used to imply a fact but does not directly prove it (finding a suspect's gun at a crime scene is circumstantial evidence that the suspect was at the crime scene) The more circumstantial evidence there is, the greater weight it carries
  • Physical: synthetic fibers, weapons, bullets, shell casings, paint chips, documents, imprints, and prints, shoe prints, tire marks, tool marks, soil, drugs, ect
  • Biological: body or body parts, body fluids, hair, leaves, plant parts, natural fibers, feathers, wood
  • Trace: small but measurable amounts of physical or biological material found at a crime scene (strand of hair, fingerprints, DNA, drop of blood, pollen, gunshot residue)
  • Class Evidence: narrows evidence to a group of persons or things, can be used to exclude some suspects (blood type can be A, B, AB, or O - By finding one type at a crime scene, the suspects will be narrowed down to a smaller group)
    • May become individual based on how small of a group it can be pinned on
  • Individual Evidence: narrows evidence down to a single person or thing (fingerprints, handwriting, DNA and physical matches)
• Importance of evidence
  • Can prove a crime has been committed and set the scene for the investigation
  • Can back up witness testimony or prove it to be false
  • Can link a suspect with a victim or with a crime scene
  • Can determine the identity of people associated with a crime
• Crime Scene Investigation Team
  • First Police Officer on the scene
  • Backup Police and possibly a district attorney
  • Medics
  • Investigator/Detective
  • Medical Examiner
  • Photographer and/or Field Evidence Technician
  • Lab Experts
• Seven S's of Crime Scene Investigation
  • Secure the scene
    • The first responding police officer must make sure the scene is secure by first making sure all individuals in the area are safe and second by preserving evidence.
    • Obtain medical assistance if needed
    • Arrest suspects
    • Isolate the area
    • Request additional needs for investigators
  • Separate the witnesses
    • Witnesses must not be allowed to talk to one another. This prevents them from working together to create a story (collusion).
  • Scan the scene
    • Forensic examiners scan the scene to see where photos should be taken. The primary and secondary crime scenes must be determined.
      • The primary crime scene is where a crime actually occurred.
      • A secondary crime scene is in some way related to the crime but is not where the actual crime took place.
  • See the scene
    • A crime scene examiner looks at the scene. The Photography Unit takes photos of the overall area and close up photos with and without a measuring ruler.
  • Sketch the scene
    • North should be labeled and a scale of distance should be included
    • All important objects (weapon and body) should be measured from two immovable landmarks
    • Any other objects in the vicinity of the crime should be included in the sketch (ex. Doors, windows, furniture, trees, vehicles, etc.)
    • Also include: Date, time, location, case number, and names of individuals involved (Sketched by and Verified by)
  • Search for evidence
    • Spiral, Grid, Linear, Quadrant or Zone
  • Secure and collect evidence
    • All evidence must be properly packaged, sealed and labeled using specific techniques and procedures.
    • Packaging Evidence
      • Metal or plastic forceps may have to be used to pick up small items.
      • Plastic pill bottles with lids are preferred containers for hairs, glass, fibers, and other kinds of trace evidence.
      • Liquids and arson remains are stored in airtight, unbreakable containers.
    • Druggist's Fold for evidence
      • Most biological evidence is stored in breathable containers so the evidence can dry out, reducing the chances of mold contamination. After the evidence has air dried, it is packaged into a paper bindle (or druggist’s fold) then placed in a paper or plastic container.
    • Evidence Log and Chain of Custody
      • Each person who comes in contact with a piece of evidence must use proper procedure and protocol in order to maintain responsible handling of evidence from crime scene to courtroom in order for the evidence to be admissible in court.
    • Control Samples
      • Control samples should also be taken from the victim for purposes of exclusion (blood, hair, etc.)
      • Standard/Reference Sample- Physical evidence whose origin is known, such as blood or hair from a suspect, that can be compared to crime-scene evidence.
  • Analyze the Evidence
    • A forensic lab processes all evidence the crime scene investigation team collected.
    • Forensic lab technicians are specialized and process one type of evidence, unlike CSI TV shows where they may process many.
  • Crime Scene Reconstruction
    • Crime scene reconstruction allows the detectives to form a hypothesis of the sequence of events from before the crime was committed through its commission.
  • Legal Considerations
    • Any removal of evidence from a crime scene must be in accordance with the Fourth Amendment.
    • “The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized.”
  • A warrantless search can be conducted:
    • under emergency circumstances (danger to life or limb)
    • if there is immediate danger of the loss or destruction of evidence
    • if there is probable cause — the search of a person and their immediate property in conjunction with a lawful arrest
    • with the consent of the involved parties