CSI and Evidence

Principle of Exchange Dr. Edmond Locard, director of the world’s first forensic lab (1910, Lyon, France), established the idea of the exchange principle; namely that: When a person comes in contact with an object or another person, a cross-transfer of physical material can occur. Study of the material can determine the nature and duration of the transfer. Forensic Science: Fundamentals & Investigations, Chapter 2

The Crime Scene Investigation Team Who is at the crime scene? Police and possibly a district attorney. Crime scene investigators. Medical examiners. Detectives. Specialists. Forensic Science: Fundamentals & Investigations, Chapter 2

The Seven S’s of Crime Scene Investigation Secure the scene Separate the witnesses. Scan the scene. See to it that the crime scene examiners receive overall and close up photos with and without measuring rulers. Sketch the scene. Search for evidence. Secure the collected evidence. Forensic Science: Fundamentals & Investigations, Chapter 2

Securing Preserve and protect the area Exclusion of unauthorized personnel Isolate the area Separate the witnesses. Scan the scene. See to it that the crime scene examiners receive overall and close up photos with and without measuring rulers. Forensic Science: Fundamentals & Investigations, Chapter 2

Recording the Scene Very important to document the condition of the scene and to delineate the location of physical evidence. Photography, sketches, and notes are the 3 methods for crime-scene recording Must be very detailed throughout the process Forensic Science: Fundamentals & Investigations, Chapter 2

Photography All objects must be photographed from all angles before moving anything If items are moved, positions changed, or items added, the photographs may NOT be admissible in court When the size of an item is significant , a ruler may be inserted near the object and included in the photo as a frame of reference. Every photo, positioning, angles, and movement of the photographer should be recorded in the notes along with detailed pictures and descriptions of the scene, adjacent, areas, entrances and exits, and any other evidence Forensic Science: Fundamentals & Investigations, Chapter 2

Sketching the Scene Rough Sketch A Rough sketch must contain an accurate depiction of the dimensions of the scene and show the locations of all objects. Objects are located in the sketch by distance measurements from 2 fixed points, such as the walls of a room. All measurements must be accurate with no estimations A legend is placed below the sketch that correlates the item letter or number to the description. There should be a compass heading designating North Finished Sketch Must reflect information from the rough sketch in order to be admissible evidence in court. Forensic Science: Fundamentals & Investigations, Chapter 2

Forensic Science: Fundamentals & Investigations, Chapter 2

Forensic Science: Fundamentals & Investigations, Chapter 2

Types of Evidence Statements of a witness in court would be direct evidence. Indirect or circumstantial evidence, such as a fingerprint (physical evidence) or blood or hairs (biological evidence), would imply something, and is called trace evidence. Forensic Science: Fundamentals & Investigations, Chapter 2

Examples of Trace Evidence Pet hair on clothes or rugs Fingerprints on a glass Soiled tracks in the house Blood on a shirt Used Tissue Paint chips Forensic Science: Fundamentals & Investigations, Chapter 2

Types of Evidence Evidence taken from a crime scene. Direct or circumstantial evidence? Physical or biological evidence? Class or individual evidence? Explain why this would be or would not be trace evidence. Forensic Science: Fundamentals & Investigations, Chapter 2

Search for Evidence Investigator in charge assigns personnel to search a scene If possible, one person should supervise and coordinate the collection of evidence May subdivide the scene into segments and search individually or the search may start at the outward points and gradual move toward the center in a circular fashion The methods used should be documented along with steps within the scene Forensic Science: Fundamentals & Investigations, Chapter 2

Forensic Science: Fundamentals & Investigations, Chapter 2

Evidence Collection Integrity of evidence MUST be maintained when an item is collected All clothing MUST be placed in air-dried containers and placed in separate bags to ensure constant circulation of air Bloodstained materials should be in airtight containers to prevent the accumulation of moisture produces mold and mildew **If additional evidence needs to be collected after the initial timeframe, a search warrant must be presented. Forensic Science: Fundamentals & Investigations, Chapter 2

Packaging the evidence – “druggist fold” Crease a clean paper and place the evidence in the X position (as shown above). Fold in the left and right sides, and then fold in the top and bottom. Put the bindle into a plastic or paper evidence bag affixing a seal over the opening. Write your name on the seal. Used for small amounts of trace evidence Forensic Science: Fundamentals & Investigations, Chapter 2

Chain of Custody In order to present credible evidence in court, a chain of custody log is essential. A person bags the evidence, marks it for identification, seals it, and signs it across the sealed edge (above, left). They must also include the location and date collected. It is signed over to a technician in a lab for analysis who opens it, but not on the sealed edge. After analysis, the technician puts it back in the evidence bag, seals it in another bag, and signs the evidence log (above, right). Every individual who possesses the evidence must maintain a written record of its acquisition and deposition. Forensic Science: Fundamentals & Investigations, Chapter 2

Analyze the Evidence The facts of the case are determined when the forensic lab processes all the collected evidence. The lab then sends the results to the lead detective who aims to see how it all fits into the crime scenario. Forensic Science: Fundamentals & Investigations, Chapter 2

Analyze the Evidence The lab results can: Show how reliable are any witness accounts. Establish the identity of suspects or victims. Show suspects to be innocent or link them with a scene or victim. Forensic Science: Fundamentals & Investigations, Chapter 2

Crime Scene Reconstruction Crime scene reconstruction involves: forming a hypothesis of the sequence of events from before the crime was committed through its commission. Forensic Science: Fundamentals & Investigations, Chapter 2

Staged Crime Scenes When the lab results do not match up with the testimony of witnesses, it can mean the crime was staged; common examples include: Staging a fire—to cover bankruptcy. Staging a suicide—to cover a murder. Staging a burglary—to collect insurance money. Forensic Science: Fundamentals & Investigations, Chapter 2

Staged Crime Scenes To help determine whether a crime scene was staged, consider: Whether the type of wound found on the victim matches the weapon employed. Whether the wound could have been easily self-inflicted. The mood and actions of the victim before the event. The mood and actions of a suspect before the event. Forensic Science: Fundamentals & Investigations, Chapter 2