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Saturday, November 18, 2023

Forensic Science

     The principle role of the forensic scientist is to identify physical crime scene evidence by comparing it to known samples obtained either from a suspect's person or from an object such as a gun, shoe or burglar tool that this person possessed, wore or was associated with. Forensic science relies on the principle that criminals leave part of themselves at the scene of the crime. Evidence left at the site of a crime might include blood, semen, latent fingerprints, shoe impressions, bite marks, hair follicles and textile fibers. Moreover, the suspect will often inadvertently take something away from the crime scene. A criminal might, for example, leave the crime site carrying traces of the victim's blood and tissue under his fingernails.

     The theory that a criminal perpetrator leaves a part of himself at the scene of a crime and takes a piece of the crime site with him was postulated by Edmund Locard, who in 1911 in Lyon, France, established the world's first crime lab. Referred to as the Locard Exchange Principle, this idea, along with the need to reconstruct what took place at the site of a criminal act, is the basic rationale behind crime scene investigation. The term "associative evidence" describes traces of things that, pursuant to the Locard Exchange Principle, associates a person to the site of the offense.

     Simply put, forensic science involves the application of hard science and technology to the investigation of crime, the proof of guilt or innocence at a criminal trial and the resolution of factual issues in civil litigation. The most widely used components of forensic science are forensic chemistry, toxicology, biology, mineralogy, serology (bodily fluids), anthropology (bones), pathology (autopsies and cause and manner of death) and odontology (identification by teeth). The process of firearms identification, once called forensic ballistics, incorporates knowledge and science in a variety of fields including gun-smithing, ordnance, ballistics, chemistry, metallurgy, microscopy, photography and the forensic pathology of gunshot wounds. Latent fingerprint identification and forensic document examination--the identification of unknown handwriting and the analysis of paper, ink and printing instruments--are also within the forensic science field. Blood spatter interpretation and identification by human bite mark impressions, while often treated as forensic science, are not hard science and should not be considered as such.

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