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Crime Scene Investigation Essentials

Learn about securing, examining, and searching crime scenes, including legal considerations, evidence types, and sketching techniques. Understand the importance of chain of custody and reference samples.

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Crime Scene Investigation Essentials

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  1. THE CRIME SCENE

  2. The First Steps • The first officer to arrive at the scene is responsible for securing the crime scene. • First priority should be given to obtaining medical assistance for individuals in need of it and to arresting the perpetrator. • As soon as it is possible, extensive efforts must be made to exclude all unauthorized personnel from thescene. • Once the scene is secured, the preliminary exam must begin. • Recording of the crime scene becomes a critical piece to the investigation process. THE CRIME SCENE

  3. The Preliminary Exam • A lead investigator will start the process of evaluating the area. • First, the boundaries of the scene must be determined. • Followed by the establishment of the perpetrator’s path of entry and exit. • The investigator then proceeds with an initial walk-through of the scene to gain an overview of the situation and develop a strategy for the systematic examination and documentation of the entire crime scene. • This is done before processing the crime scene for physical evidence. THE CRIME SCENE

  4. The Search • The search for physical evidence at a crime scene must be thorough and systematic. • The search pattern selected will normally depend on the size and locale of the scene and the number of collectors participating in the search. • For a factual, unbiased reconstruction of the crime, the investigator—relying upon his or her training and experience—must not overlook any pertinent evidence. • Physical evidence can be anything from massive objects to microscopic traces. THE CRIME SCENE

  5. Figure 2–7  Several typical examples of crime-scene search patterns. The pattern selected normally depends on the size and locale of the scene and the number of collectors participating in the search.

  6. Legal Considerations • Fourth Amendment • Protection against illegal search and seizure • Searches are allowed without a warrant if: • 1. in the existence of emergency circumstances • 2. the need to prevent immediate loss or destruction of evidence • 3. a search of a person or property within the immediate control of the person during a lawful arrest • 4. the involved parties give consent

  7. Physical evidence: any object that can establish that a crime has been committed or can provide a link between a crime and its victim or between a crime and its perpetrator • Rough sketch: a draft representation of all essential information and measurements at a crime scene. This sketch is drawn at the crime scene • Finished sketch: a precise rendering of the crime scene, usually drawn to scale

  8. Chain of custody: a list of all persons who came into possession of an item of evidence • Control: physical evidence whose origin is known, such as blood or hair from a suspect that can be compared to crime-scene evidence (AKA reference sample) • Buccal swab: swab of inner portion of cheek; cheek cells are usually collected to determine the DNA profile of an individual

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