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Chapter 2 Forensic Science
Forensic Science (CHEM1118)
Fairleigh Dickinson University
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The Crime Scene
● Processing the Crime Scene ○ Crime labs “run” on Physical Evidence. ○ 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. ● Secure and Isolate the Crime Scene ○ It is the responsibility of the first officer arriving on the scene of a crime to take steps to preserve and protect the area to the greatest extent possible. ● Record the Scene ○ The opportunity to permanently record the scene in its original state must not be lost. ○ Such records will not only prove useful during the subsequent investigation but are also required for presentation at a trial in order to document the condition of the crime site and to delineate the location of physical evidence. ● Photography ○ The most important prerequisite for photographing a crime scene is for it to be in an unaltered condition. ○ Unless there are injured parties involved, objects must not be moved until they have been photographed from all necessary angles. ● Sketches ○ Once photographs are taken, the crime-scene investigator will sketch the scene. ○ 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. ● Notes ○ Note taking must be a constant activity throughout the processing of the crime scene. ○ These notes must include a detailed written description of the scene with the location of items of physical evidence recovered. ○ They must also identify the time an item of physical evidence was discovered, by whom, how, and by whom it was packaged and marked, and the disposition of the item after it was collected. ● Conduct a Systematic Search for Evidence ○ The search for physical evidence at a crime scene must be thorough and systematic. ○ For a factual, unbiased reconstruction of the crime, the investigator, relying upon his or her training and experience, must not overlook any pertinent evidence. ○ The following are to be collected and sent to the forensic lab:
■ Victims clothing ■ Fingernail scrapings ■ Head and pubic hairs ■ Blood (for DNA typing purposes) ■ Vaginal, anal, and oral swabs (in sex-related crimes) ■ Recovered bullets from the body ■ Hand swabs from shooting victims (for gunshot residue analysis.) ● Collect and Package Physical Evidence ○ Physical evidence must be handled and processed in a way that prevents any change from taking place between the time it is removed from the crime scene and the time it is received by the crime lab. ○ Each different item or similar items collected at different locations must be placed in a separate container. Packaging evidence separately prevents damage through contact and prevents cross-contamination. ● Maintain Chain of Custody ○ Continuity of possession must be established whenever evidence is presented in the court as an exhibit. ○ Chain of Custody ■ A list of all persons who came into possession of an item of evidence. ● Obtain Standard/Reference Samples ○ The examination of evidence, whether it is soil, blood, glass, hair, fibers, and so on, often requires comparison with a known standard/reference sample. ○ Standard/Reference Sample ■ Physical evidence whose origin is known, such as blood or hair from a suspect, that can be compared to crime-scene evidence. ○ Buccal Swab ■ Swab of inner portion of cheek; cheek cells are usually collected to determine the DNA profiling of an individual. ○ Substrate Control ■ Uncontaminated surface material close to an area where physical evidence has been deposited. This sample is to be used to ensure that the surface upon which a sample has been deposited does not interfere with laboratory tests. ● Submit Evidence to the Laboratory ○ Evidence is usually submitted to the laboratory either by personal delivery or by mail shipment. ○ The method of transmittal is determined by the distance the submitting agency must travel to the laboratory and the urgency of the case. ● 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. ● Legal Considerations at the Crime Scene
Chapter 2 Forensic Science
Course: Forensic Science (CHEM1118)
University: Fairleigh Dickinson University
