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PHYSICAL EVIDENCE

PHYSICAL EVIDENCE. Chapter 3. Physical Evidence. Objectives: Review the common types of physical evidence encountered at a crime scene Explain the difference between the identification and comparison of physical evidence.

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PHYSICAL EVIDENCE

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  1. PHYSICAL EVIDENCE Chapter 3

  2. Physical Evidence Objectives: • Review the common types of physical evidence encountered at a crime scene • Explain the difference between the identification and comparison of physical evidence. • Define and contrast individual and class characteristics of physical evidence.

  3. Green River Killer YouTube - Gary Ridgway'Green River Killer' Part 1 of 5

  4. Blood, semen, and saliva Documents Drugs Explosives Fibers Fingerprints Firearms and ammunition Glass Hair Impressions Organs and physiological fluids Paint Petroleum products Plastic bags Plastic, rubber, and other polymers Powder residues Soil and minerals Tool marks Vehicle lights Wood and other vegetative matter Types of Physical Evidence PHYSICAL EVIDENCE

  5. Purpose of Examining Physical Evidence • Physical evidence is examined for identification or comparison purposes. • Identification – the process of determining a substance’s physical or chemical identity • Comparison – the process of ascertaining whether two or more objects have a common origin PHYSICAL EVIDENCE

  6. Identification Examples • Chemical compositions of substances that are illicit drugs. • Residue from a fire or explosion • identification of blood, semen, hair, or wood PHYSICAL EVIDENCE

  7. Comparison Examples • A hair found at a crime scene may match a hair sample taken from a suspect • A paint chip found on a hit-and-run victim’s clothing may match paint taken from s suspects vehicle PHYSICAL EVIDENCE

  8. Comparison Characteristics • Individual Characteristics • Evidence that can be associated to a common single source with an extremely high degree of probability • Never 100 % certain • High degree of probability PHYSICAL EVIDENCE

  9. Individual Characteristics • Examples: • fingerprints • random striation markings on bullets or tool marks • irregular and random wear patterns in tire or footwear impressions • handwriting characteristics • the fitting together of the irregular edges of broken objects as in a jigsaw puzzle • matching sequentially made plastic bags by striation marks running across the bags PHYSICAL EVIDENCE

  10. Class Characteristics • Class Characteristics -evidence that can be associated only with a group and not with a single source • Examples: -Blood types -Paint from a car -clothing fibers -carpet fibers PHYSICAL EVIDENCE

  11. Using Physical Evidence • As the number of different objects linking an individual to a crime scene increases, so does the likelihood of that individual’s involvement with the crime. • Just as important, a person may be exonerated or excluded from suspicion if physical evidence collected at a crime scene is found to be different from standard/reference samples collected from that subject. PHYSICAL EVIDENCE

  12. Forensic Databases • IAFIS-The Integrated Automated Fingerprint Identification System; a national fingerprint and criminal history system maintained by the FBI. (1999) • CODIS – The Combined DNA Index System; enables federal, state, and local crime laboratories to electronically exchange and compare DNA profiles; maintained by FBI (1998) • NIBIN - The National Integrated Ballistics Information Network; allows firearm analysts to acquire, digitize, and compare markings made by a firearm on bullets and cartridge casings. (ATF) • PDQ- The International Forensic Automotive Paint Data Query; database contains chemical and color information pertaining to original automotive paints. (RCMP) • SICAR- shoeprint image capture and retrieval; a shoeprint database.

  13. Physical Evidence Objective: • Explain the purpose physical evidence plays in reconstructing the events surrounding the commission of a crime.

  14. Crime Scene Reconstruction • Reconstruction-the method used to support a likely sequence of events at a crime scene by observing and evaluating physical evidence and statements made by those involved with the incident • The collection and documentation of physical evidence plays a crucial role in reconstructing the events that took place surrounding the crime. PHYSICAL EVIDENCE

  15. Crime Scene Reconstruction Who is involved in reconstruction? • Medical examiners • Criminalists/crime scene investigators • Law enforcement

  16. Reconstruction Examples • Determining whether a body was moved after death • Determining whether a victim was clothed at the time of death • Analyzing bullet trajectory • Analyzing blood spatter • Determining the direction from which projectiles penetrated glass objects • Estimating distance of a shooter from a target • Locating gunshot residues on a suspect

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