Presentation on theme: "Crime-Scene Investigation and Evidence Collection."— Presentation transcript:
Crime-Scene Investigation and Evidence Collection
Are there cars parked on the sides of the road? What color is the pickup truck driving in the road? Any minivans around? What does the blue sign say? What’s the speed limit? Are there any pedestrians on the road?
Locard’s Exchange Principle When a person comes into contact with an object or another person, a cross-transfer of physical evidence can occur Hair, skin cells, clothing fibers, pollen, glass fragments, debris from clothing, makeup, soil Called trace evidence pet hair on clothes Hair on your brush Fingerprints on glass Soil tracked into house Drop of blood on t-shirt Used tissue Paint chips Broken glass Fiber from clothing
Evidence Classified two different ways – Direct evidence Circumstantial evidence Physical evidence Biological evidence Trace evidence
Direct Evidence Firsthand observations such as eyewitness accounts or police dashboard video cameras Confessions Testimony by a witness in court
Circumstantial Evidence Indirect evidence that can be used to imply a fact but that does not directly prove it Link between crime scene and a suspect Physical – Impressions, fingerprints, footprints, shoe prints, tire impressions, tool marks, fibers, weapons, bullets, shell casings Reduces number of suspects to a specific, smaller group Biological – body fluids, hair, plant parts, natural fibers Makes the group of suspects very small, or reduces it to a likely individual
Class vs. Individual Evidence Class – narrows identity to a group of persons or things Ex – blood type Individual – narrows an identity to a single person or thing Ex – fingerprints
The CSI Team Police officers District attorney Crime scene investigators Medical examiners Detectives Specialists
The Crime Scene Investigation Team Police officers – secure the scene District attorney – determine whether search warrant is necessary Crime-scene investigators – document crime scene in detail and collect physical evidence Recorders, sketch artists, photographers, evidence collectors Medical examiners – determine cause of death if homicide Detectives – look for leads by interviewing witnesses and talking to crime-scene investigators about evidence Specialists – consulted if the evidence requires their expertise Entomologists, forensic scientists, forensic psychologists, etc.
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
1. Securing the Scene Responsibility of the first responder (usually a police officer) Restricts all persons not authorized from entering Security log of all entering and exiting May request various experts to be sent to scene First Priority – safety of all individuals Second Priority – preservation of evidence
2. Separating Witnesses Witnesses must not be allowed to talk to one another! Questions to ask: When did the crime occur? Who called in the crime? Who is the victim? Can the perpetrator be identified? Where were you when you observed the crime scene?
3. Scanning the Scene Scan the scene to determine where photos should be taken Primary crime scene – where crime took place Secondary crime scene – location linking to crime Ex: Primary scene - front of store where robbery took place Secondary scene – home of suspect Ex: Primary scene – location of murder Secondary scene – location where corpse was found
4. Seeing the Scene Crime examiner needs to see whole scene NEEDS TO BE IN UNALTERED POSITION!!! Photos of overall area Close-up photos Photos with and without a measuring ruler View of crime scene from different angles and distances Close-up photos of any evidence and bodies Photos need to be taken before evidence or body is moved
5. Sketching the Scene Rough sketch – notes position of body and any other evidence All objects measured from two immovable landmarks North should be labeled, scale included for distance Doors, windows, furniture If outdoors, position of trees, vehicles, hedges, other structures Drawn AT the scene Also include – name, date, location, conditions outside or inside
Figure 2–4 Rough-sketch diagram of a crime scene. Courtesy Sirchie Finger Print Laboratories, Inc., Youngsville, N.C.,
5. Sketching the Scene Final Sketch – include all the aspects of a rough sketch but more accurate Possible for presentation in court Computer programs available now Drawn in the lab AFTER searching the crime scene Note-taking also occurs throughout entire process
Figure 2–5 Finished- sketch diagram of a crime scene. Courtesy Sirchie Finger Print Laboratories, Inc., Youngsville, N.C.,
6. Searching for evidence Scene should be walked and location of evidence marked, photographed, and sketched Patterns: Spiral Grid Linear Quadrant or Zone Single investigator – grid, linear, or spiral pattern Group of investigators – linear, zone, quadrant
7. Securing and Collecting Evidence All must be properly packaged, sealed, and labeled Liquids and arson – stored in airtight, unbreakable container Biological evidence – stored in breathable containers so air can dry out Wet evidence – stored in paper and allowed to air dry NEVER place wet evidence in an airtight container; will cause mold and degrade DNA Paper bindle – paper used to store evidence Placed into evidence bag and labeled
Standards There are many standards for collecting different types of evidence Example: National Institute of JusticeNational Institute of Justice
Control Samples Obtained from the victim for the purpose of exclusion Ex - blood samples found on a victim or at crime scene compared to victim’s blood If they match, sample is victims and no further tests run If not, may have come from suspect and further testing is completed!
Evidence Log Case number Item inventory number Description of evidence Name of suspect Name of victim Date and time of recovery Signature of person recovering evidence Signature of any witnesses present during collection
Chain of Custody Each person who handles the evidence must be recorded properly 1. When evidence is found – marked with proper information and placed in a collection bag 2. Container is sealed and collector’s signature is written across sealed edge 3. Next person responsible opens at a location other than sealed edge, completes exam, reseals in new packaging and signs chain of custody log! 4. Pattern continues!
Chain of Custody EXTREMELY important for courtroom! All who handled evidence could be asked to appear in court Process must show evidence was handled properly and every person handling it was recorded
Analyze the Evidence FBI crime lab is one of largest forensic labs in the world! Forensic Lab Technicians – specialized and process only one type of evidence Lead detective – lab results sent to him Looks at evidence and attempts to determine how it fits into overall crime scenario Must consider all possible interpretations for evidence
Use of Evidence Evidence compared to witness’ statements Can link a suspect to scene or a victim Establish the identity of a victim Confirm verbal witness testimony Acquit the innocent
Crime Scene Reconstruction Forms a hypothesis of the sequence of events from before the crime was committed through its commission Evidence does not lie, but could be staged! Evidence is used to determine overall crime scenario
54 Crime Scene Safety The increasing spread of AIDS and hepatitis B has sensitized the law enforcement community to the potential health hazards that can exist at crime scenes. In reality, law enforcement officers have an extremely small chance of contracting AIDS or hepatitis at the crime scene. The International Association for Identification Safety Committee has proposed guidelines to protect investigators at crime scenes containing potentially infectious materials that should be adhered to at all times.
55 Crime Scene Safety 1. At crime scenes where blood or body fluids involved: latex gloves and shoe coverings should be warn. 2. If potentially infectious dust or mist encountered: particle mask/ respirator, goggles, or face shield recommended also. 3. Personnel should be aware of sharp objects, knives, hypodermic syringes, razor blades, etc and place them in appropriate container with label. 4. Red biohazard bag should be used for disposal of contaminated gloves, clothing, masks, pencils, etc. and removal to approved biohazardous waste pickup.
56 Crime Scene Safety 5. Note-taking should be done while wearing uncontaminated gloves to avoid contamination or pens, pencils, notebook, paper, etc. 6. If personal protective equipment (PPE) becomes torn, must be removed immediately and person must decontaminate the potentially contaminated body area with recommended solution. 7. No eating, drinking, smoking, or applying makeup at scene of a crime. 8. All nondisposable items (lab coats, towels, personal clothing) that may be contaminated are placed in a yellow plastic bag, labeled “Infectious Linen” and laundered by a qualified service.