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Sherlock Holmes, a fictional detective of a century ago, was one of the first to use forensic science—the scientific analysis of physical evidence to solve crimes. Holding a big magnifying glass, Holmes inspected crime scenes for footprints, broken glass. hair—anything that might help identify the person who committed the crime. In today's world, Holmes might be a CSI, or crime scene investigator. Today, when a crime is reported, a murder for instance, the police immediately send a medical examiner (ME) and a CSI team to the crime site. The ME and CSIs will be part of a panel of technical experts in the investigation. At the crime scene, the ME examines the body of the victim and looks for wounds or marks that might be related to the crime. The ME also takes many photographs of the body. The body is subsequently taken away for a detailed examination that will establish the cause and time of the victim's death.
Meanwhile, CSIs first take hundreds of photographs of the crime site. Next they check the site for fingerprints. Most fingerprints form when sweat or another oily substance on a fingertip leaves an invisible imprint on a glass. tabletop, or other object. CSIs dust a black powder on objects at the crime site to make these prints visible. The CSI's then look for drops of blood, strands of hair, pieces of ripped cloth or other evidence that might link someone to the crime site.
"Every contact leaves a trace," according to an authority in forensics, This means that whenever a crime involves physical contact, the criminal either leaves something at the site, takes something from the site. or both. This might be any number of substances. including hair, animal fur, sand, grass, and fibers from clothing of carpeting. Such trace evidence is usually difficult to detect, so. like Sherlock Holmes CSIs rely on handheld magnifying glasses to examine the crime scene. CSIs might even vacuum the entire area to collect tiny samples. They carefully label each piece of evidence as they collect it. The collected evidence is then sent to a forensics laboratory. There, forensic scientists will analyze it to establish how and when the murder took place, where it took place, and who did it. Sometimes the evidence will even show why it took place, that is, the motive for the killing.
Among all the evidence found at the site, fingerprints are conclusive in linking a specific person to the crime scene.This is because no two people have the same fingerprints. Fingerprints from a crime scene are analyzed by computer to determine if they match the prints of a known criminal or crime suspect. DNA is another conclusive means of identification because each person's DNA is unique. DNA is contained in cells of the body so that evidence of hair, blood, tears, sweat, or other bodily fluids found at a crime scene can be used to link a specific person to the crime. Like fingerprints, DNA samples are analyzed by computer to determine if they match the DNA of a known criminal or a suspect.
Voices, too, are unique. Samples of voices from security camera tapes, telephone answering machines, or other recording devices can be scanned electronically. A printout of the scan will show patterns of highs and lows, rhythm, and volume that can be compared to patterns of a suspect's voice. However, authorities have contrary opinions about using voiceprints for identification. Some argue that voices can change over time as people age or suffer illnesses, so old voiceprints are not always reliable. In the laboratory; forensic scientists use an electron microscope to scan samples of the substances that were collected at the crime scene. Then they enlarge the samples (up to 150,000X) on a visual display unit. This allows them to easily compare those samples with samples found at another location or on a suspect's clothing. Forensic laboratories have on file the shoe print patterns of thousands of kinds of shoes. These can be compared to shoeprints found at a crime scene to establish the size and kind of shoes worn by a suspect. If the shoeprint was made in a soft material, like mud, the lab may be able to tell the height and weight of the person by the depth of each step and the distance between steps.
After all of the evidence has been analyzed, the police chief consults with panel members. Based on the evidence, they determine if it is logical to accuse and arrest a crime suspect. If it is, members of the panel may later be asked to present their forensic evidence in a court of law as proof of a suspect's guilt.