Successfully reported this slideshow.
We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. You can change your ad preferences anytime.

CSI and Evidence Collection

1,479 views

Published on

CSI and Evidence Collection

Published in: Science
  • Be the first to comment

CSI and Evidence Collection

  1. 1. Chapter 2. Crime-Scene Investigation and Evidence Collection
  2. 2. Chapter 2. Crime-Scene Investigation and Evidence Collection Introduction  Objectives  Summarize Locard’s exchange principle  Identify four examples of trace evidence  Distinguish between direct and circumstantial evidence  Identify the type of professionals who are present at a crime scene  Summarize the seven steps of a crime-scene investigator  Explain the importance of securing the crime scene  Identify the methods by which a crime scene is documented  Demonstrate the proper technique in collecting and packaging trace evidence  Describe how evidence from a crime scene is analyzed
  3. 3. Chapter 2. Crime-Scene Investigation and Evidence Collection Introduction  A single hair or clothing fabric can lead police to a responsible person  The goal of a crime scene investigation is to recognize, document, and collect evidence at the scene of a crime.
  4. 4. Chapter 2. Crime-Scene Investigation and Evidence Collection Principle of Exchange  Whenever two people come into contact with each other a physical transfer occurs.  Pet hair on your clothes or rugs  Hair on your brush  Fingerprints on glass  Soil tracked in  A drop of blood  Paint chips  Broken glass  A fiber from clothing  These transferred materials are considered trace evidence.  First noticed by Dr. Edmond Locard  Locard’s Exchange principle states that when a person comes into contact with an object or another person, a cross-transfer of physical evidence can occur.  Intensity, duration, and nature of the materials can determine extent of transfer.
  5. 5. Chapter 2. Crime-Scene Investigation and Evidence Collection Types of Evidence  Direct evidence  First hand observation (eyewitnesses or video)  Confessions  Circumstantial evidence  Indirect evidence, only actually seen left behind by the suspect and victim  Can be physical or biological
  6. 6. Chapter 2. Crime-Scene Investigation and Evidence Collection Types of Evidence  Examples of Physical evidence  Fingerprints  Footprints  Shoe prints  Tire impressions  Tool marks  Fibers  Weapons  Bullets  Shell casings
  7. 7. Chapter 2. Crime-Scene Investigation and Evidence Collection Types of Evidence  Examples of Biological Evidence  Body fluids  Hair  Plant parts  Natural fibers  Reduces suspects to a very small number, or likely individual
  8. 8. Chapter 2. Crime-Scene Investigation and Evidence Collection Types of Evidence  Trace evidence  Circumstantial evidence  Hair found on a brush, fingerprints on a glass, blood drops on a shirt, soil tracked in to a house on shoes  Class evidence  Narrows an identity to a group of persons or things  Ex. Blood typing  Individual evidence  Narrows an identity to a single person or thing.  Ex. Fingerprint
  9. 9. Chapter 2. Crime-Scene Investigation and Evidence Collection The Crime Scene Investigation Team  Police officers  First to arrive, may need a district attorney to obtain a search warrant  Crime scene investigators  Document the crime scene, collect physical evidence, record data, sketch the scene, and photograph the scene  Medical examiners (coroners)  Determine time of death when a homicide occurs  Detectives  Interview witnesses and talk to crime scene investigators about the evidence  Specialists  Ex. Entomologists, forensic scientists, and forensic psychologist
  10. 10. Chapter 2. Crime-Scene Investigation and Evidence Collection The Seven S’s of Crime Scene Investigation 1. Securing the scene 2. Separating the witnesses 3. Scanning the scene 4. Seeing the scene 5. Sketching the scene 6. Searching for evidence 7. Securing and collecting evidence
  11. 11. Chapter 2. Crime-Scene Investigation and Evidence Collection Securing the Scene  Securing the scene is the responsibility of the first responding police officer (first responder)  Priorities  Safety of all individuals in the area  Preservation of evidence  Transfer, loss, or contamination of evidence can occur if left unsecured.  Security log will be kept for all those entering the crime scene  Request any other additional needs.
  12. 12. Chapter 2. Crime-Scene Investigation and Evidence Collection Separating the Witnesses  Witnesses must not be allowed to talk to each other  Their accounts must be compared  Prevention of witnesses working together to create a story (collusion)  Possible questions:  When did the crime occur?  Who called in the crime?  Who is the victim?  Can the perpetrator be identified?  What did you see happen?  Where were you when you observed the crime scene?
  13. 13. Chapter 2. Crime-Scene Investigation and Evidence Collection Scanning the Scene  Scan the scene to determine where pictures should be taken.  Determine primary and secondary scene.  Ex. A murder may have taken place at one location (primary scene) and the corpse found at another (secondary scene)
  14. 14. Chapter 2. Crime-Scene Investigation and Evidence Collection Seeing the Scene  Photos of the overall area and close-up photos with and without a measuring ruler should be taken.  Why is the ruler necessary?
  15. 15. Chapter 2. Crime-Scene Investigation and Evidence Collection Sketching the Scene  Note position of body (if any) and any other evidence  All objects should be measured from two immovable objects  North should be indicated  Scale should be included  Doors, windows, and furniture should be included  If outside, trees, vehicles, or other objects should be included  Later, a more accurate and final copy will be created for use in court.
  16. 16. Chapter 2. Crime-Scene Investigation and Evidence Collection Searching for Evidence  Four crime scene search patterns  Grid  Linear  Quadrant or Zone  Spiral  Ensure no area is left unsearched  May need additional light sources (example flashlight)  May need the use of forceps
  17. 17. Chapter 2. Crime-Scene Investigation and Evidence Collection Securing and Collecting Evidence  All evidence needs to be properly packaged, sealed and labeled.  Wet evidence must be dried (prevent the growth of mold and the degenerating of DNA)  Evidence is packaged in a paper bindle.  Placed in a plastic or paper container, and then sealed with tape and labeled with the signature of the collectorAlso •Name of suspect and victim •Signature of person recovering the evidence •Signature of any witnesses present during collection
  18. 18. Chapter 2. Crime-Scene Investigation and Evidence Collection Packaging Evidence 1. Choose the appropriate-size sheet of clean paper for the bindle. 2. Crease the paper as shown on page 27. 3. Place evidence in the X location. 4. Fold left and right sides in. 5. Fold in top and bottom. 6. Insert the top flap into the bottom flap then tape close. 7. Place bindle inside a plastic or paper evidence bag.. Fold the bag closed. 8. Place a seal over the folded edge of the evidence bag. 9. Have the collector write his or her name over the folded edge. Also, control samples must be obtainted for the purpose of exclusion.
  19. 19. Chapter 2. Crime-Scene Investigation and Evidence Collection Chain of Custody Then: 10. The container is given to the next person responsible for its care. 11. It is taken to the lab to a technician who opens the packaged for examination at a location other than the sealed edge. 12. It is repackaged in the original packaging and is resealed. The technician would then sign the chain of custody log.
  20. 20. Chapter 2. Crime-Scene Investigation and Evidence Collection DNA Collection and Packaging  At many crime scenes DNA evidence can be the most useful  Why?
  21. 21. Chapter 2. Crime-Scene Investigation and Evidence Collection DNA Collection and Packaging  The most common places to find DNA evidence are:  Blood  Saliva  Hair  Semen  Also found in:  Urine  Bone  Skin cells
  22. 22. Chapter 2. Crime-Scene Investigation and Evidence Collection DNA Collection and Packaging  Must identify the victim’s DNA and the DNA of anyone else who had access to the evidence.  Prosecutors must be prepared for what happens in court.  If there is any evidence that doesn’t belong to the suspect, the defense lawyer will try to claim that the DNA must point to the real perpetrator.  Therefore all DNA must be identified on all of the evidence to protect the case against the suspect.
  23. 23. Chapter 2. Crime-Scene Investigation and Evidence Collection DNA Collection and Packaging  DNA evidence needs protection from:  Contamination  Environmental damage  Degredation
  24. 24. Chapter 2. Crime-Scene Investigation and Evidence Collection Analyze the Evidence  A forensic lab processes all the evidence from the crime scene.  Lab technicians are specialized and process one type of evidence.  Results are sent to the lead detective.  A hypothesis can then be formed (sequence of events)  Evidence can:  Link a suspect with a scene or a victim  Establish the identity of a victim or suspect  Confirm verbal witness testimony  Or acquit the innocent
  25. 25. Chapter 2. Crime-Scene Investigation and Evidence Collection Crime Scene Reconstruction  Crime scene reconstruction involves forming a hypothesis of the sequence of events from before the crime was committed through its commission.  The evidence does not lie, but it could be staged.
  26. 26. Chapter 2. Crime-Scene Investigation and Evidence Collection Staged Crime Scenes  Examples:  Arson, a perpetrator stages a fire to commit another crime  Suicide/murder, a victim is murdered and the perpetrator stages the scene to look like suicide  Burglary, burglary is staged for insurance money
  27. 27. Chapter 2. Crime-Scene Investigation and Evidence Collection Review 1. Locard’s exchange principle implies all of the following except: 2. Transfer evidence can include all of the following except: 3. The reason it is important to separate the witness at the crime scene is to: 4. Correct collection of evidence requires which of the following? 5. A crime-scene sketch should include all of the following except: b. Blood spatter can be used to identify blood type a. The victim’s own blood gushing from a wound c. Prevent the witnesses from talking to each other. d. All of the above d. The type of search pattern used to collect evidence

×