Forensic investigation requires a systematic process to ensure that evidence collected at a scene is reliable and admissible in a court of law. The “7 S’s” represent a standardized protocol that guides first responders and specialized investigators through crime scene management. Adherence to these steps maintains the integrity of physical evidence, preventing contamination, destruction, or misinterpretation. This methodical approach ensures the scientific validity and legal reliability of the findings.
Securing the Scene and Witnesses
The first action upon arrival is securing the scene, which involves defining the boundaries of the area where the crime occurred and where related evidence may be located. This perimeter is established using barriers like tape or cones, creating a defined entry and exit path that minimizes scene disturbance. The goal is the immediate exclusion of unauthorized personnel, including curious bystanders and media, to prevent the accidental introduction of foreign materials or the destruction of fragile evidence like footprints or trace fibers.
Simultaneously, the second step involves separating any witnesses who are present at the location. Witnesses are kept apart to prevent collaboration or the unconscious influence of one person’s account on another’s memory. This practice ensures that each statement is an independent recollection, preserving unique details and perspectives. These initial actions are time-sensitive, often carried out by the first responding officer before specialized investigators arrive.
Detailed Documentation Methods
Once the scene is secured, the investigative team proceeds with documentation, beginning with scanning the scene, which is the third step. This initial survey is a walk-through performed by the lead investigator to gain a contextual understanding of the area and determine the scope of the investigation. The investigator mentally maps the scene and notes transient conditions, such as odors, temperatures, or lighting, before they dissipate.
The fourth step, seeing the scene, involves comprehensive photography, which creates a permanent visual record before anything is moved or touched. Investigators must capture three types of views: overall shots to show the location and its surroundings, medium-range shots to show the relationship between evidence items, and close-up shots. Close-up photographs of specific evidence must always include a scale or ruler for accurate size reference, documenting conditions like blood spatter patterns or tool marks with high resolution.
Following photography, sketching the scene provides precise spatial relationships and measurements that a two-dimensional photograph cannot accurately convey. The investigator first creates a rough sketch at the scene, which is a hand-drawn representation that includes all recovered evidence, fixed objects, and accurate measurements relative to two immovable points. Later, a finished sketch is generated, often using computer-aided design programs, to produce a refined, scale diagram suitable for court presentation.
Locating and Preserving Evidence
With the documentation complete, the sixth step involves systematically searching for evidence within the defined perimeter. Investigators employ predetermined patterns, such as the grid, strip, or zone method, to ensure a thorough and efficient examination of every surface area. The choice of search pattern depends on the size and type of the location, ensuring that no potential item of evidence is inadvertently missed during the process.
The final step is securing and collecting the physical evidence itself, which requires specialized handling and packaging techniques. Biological materials, for instance, must be air-dried and packaged in paper containers, never plastic, to prevent mold growth and degradation of DNA. Proper labeling must include the item description, location found, date, and the collector’s name, establishing the initial link in the chain of custody.
The chain of custody is a detailed written record tracking every person who has possessed an item of evidence from the moment of collection to its presentation in court. Maintaining an unbroken, documented transfer log is required, as any lapse or unaccounted handling can jeopardize the item’s integrity and lead to its inadmissibility in legal proceedings. This process ensures the evidence remains untainted and its origin is verifiable.