Trace evidence

Trace Evidence (Part I)

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• published: 02 Jun 2016
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Don't hesitate to comment below if you have any questions or additional phrases Trace Evidence(Part I) ,Summary Microscopic Analysis Types of Trace Evidence Glass Hair (fur) Fibers Paint Soil Gunshot Residue ,What is Trace Evidence? Loosely defined, trace evidence is small evidence used to link victims, suspects, objects, and crime scenes. Trace analysis uses microscopes and other instrumentation. Other sections (Drugs, Firearms) also use microscopes. ,Microscopic Analysis Who analyzes trace evidence? Labs sections are arranged differently in different labs. Different evidence could be assigned to different sections (hair:biology, fiber:chemistry) Some labs have trace or microscopy sections. ,Trace > Microscopes Using the Microscope Microscope magnifies sample. Also can look at more detailed traits of samples. Many different types of microscopes are used. ,Trace > Microscopes Microscope terminology 3-D object vs. Microscope slide 3-D object: put any object under the mic Slide: requires preparation Surface analysis vs. Look through object Surface: Looking at surface of object (normal) Or can shine light through transparent sample ,Trace > Microscopes Microscope terminology Reflected light vs. Transmitted light Refected: bounces off object (normal light) Transmitted: passes through object ,Trace > Microscopes Stereo Binocular Microscope Look at 3-D objects Usually look at surface Usually use reflected light ,Trace > Microscopes Stereo Binocular Microscope Preliminary search of objects (clothes) for small fibers, hairs, etc. Look at paint chip layers, measure fibers, bullet striations, etc. ,Trace > Microscopes Compound Microscope Can be binocular or one ocular Look at transparent object on prepared slide Look through object Use transmitted light ,Trace > Microscopes Compound Microscope Analyze fibers, hair, glass for optical traits. Biological samples for sperm cells ,Trace > Microscopes Key terms: Ocular lens Lens in the eyepiece Objective lens Lens above the sample ,Trace > Microscopes Key terms: Ocular lens Lens in the eyepiece Objective lens Lens above the sample ,Trace > Microscopes Key terms: Micrometer - “ruler” in the eyepiece, allows for measurement of sample. Magnification - Amount the object is enlarged Working Distance - Distance between the object and objective lens ,Trace > Microscopes Polarized Light Microscope (PLM) ,Trace > Microscopes Polarized Light Microscope (PLM) Takes advantage of the optical properties of glass, crystals (chemicals), and fibers. Sample absorbs light differently depending on its orientation in polarized light. ,Trace > Microscopes Comparison Microscope ,Trace > Microscopes Comparison Microscope An optical bridge allows viewing of evidence side by side. Useful for comparing bullets, fibers, hair… ,Summary of Trace Why is trace evidence useful? Collecting trace evidence Types trace evidence: Glass Hair (fur) Fibers Paint Soil Gunshot Residue ,Trace Why is Trace Evidence Useful? Can link objects and people. Object Location Victim Suspect ,Trace Object Trace evidence on hammer may include: Blood/Tissue from Victim Blood/Fingerprints from Suspect Fibers from Rug in van ,Trace Location Trace evidence on rug may include: Blood/Tissue from Victim Blood from Suspect ,Trace Victim Trace evidence on Victim may include: Blood/Semen from Suspect Fibers from Rug in van ,Trace Suspect Trace evidence on suspect may include: Blood/Tissue from Victim Fibers from Rug in van ,Trace How is Trace Evidence Transferred? Locard Exchange Principle: Whenever there is contact between two objects, they will leave or pick up debris from the other object. During a crime, there is always be a transfer of evidence. The difficulty is finding & collecting this evidence. ,Collecting Trace Evidence Who collects the evidence? Police Officer Crime Scene Investigator Forensic Scientist Depends on the state/community Often one pers