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Fs Ch 5


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Fs Ch 5

  1. 1. Physical Evidence Chapter 5
  2. 2. Physical Evidence <ul><li>Almost anything can be physical evidence </li></ul><ul><li>Important to recognize physical evidence is so that it can be collected and analyze </li></ul><ul><li>Difficult to ascertain weight of piece of evidence in court </li></ul><ul><li>-ultimately decided by a jury </li></ul>
  3. 3. Purpose of Examining Physical Evidence <ul><li>Identification: </li></ul><ul><li>-determination of the physical/chemical identity of a substance with as near absolute certainty as existing analytical techniques will permit </li></ul><ul><li>Comparison: </li></ul><ul><li>-subjects a suspect specimen and a standard/reference specimen to the same tests and examinations to determine if they have a common origin </li></ul>
  4. 4. Reference and suspect samples <ul><li>Reference/Known sample: </li></ul><ul><li>-taken from suspect </li></ul><ul><li>-the origin is known </li></ul><ul><li>Suspect sample: (NOT TAKEN FROM SUSPECT!) </li></ul><ul><li>-unknown source </li></ul><ul><li>-comes from crime scene </li></ul><ul><li>-hair/fiber from body-not victim’s </li></ul>
  5. 5. Identification <ul><ul><li>PROCESS: </li></ul></ul><ul><ul><li>-adoption of testing procedures that give characteristic results for specific standard materials </li></ul></ul><ul><ul><li>-test results have been established </li></ul></ul><ul><ul><li>-permanently recorded </li></ul></ul><ul><ul><li>-used repeatedly to prove the identity of suspect materials. </li></ul></ul><ul><ul><li>-requires number/type of tests needed to identify a substance exclude all other substances </li></ul></ul>
  6. 6. Common Types of Identification <ul><li>Illicit drugs </li></ul><ul><li>Gasoline in residues </li></ul><ul><li>Explosive residues </li></ul><ul><li>Identification of blood/semen/hair </li></ul>
  7. 7. Comparison <ul><li>Comparative analysis: </li></ul><ul><li>-if suspect specimen and a standard/reference specimen have a common origin </li></ul><ul><li>-standard/reference and suspect specimen subjected to same tests </li></ul><ul><li>2 step procedure: </li></ul><ul><li>- combinations of select properties are chosen from suspect and standard/reference specimen for comparison </li></ul><ul><li>-be prepared to render a conclusion with respect to the origins </li></ul>
  8. 8. Role of Probability <ul><li>To comprehend the evidential value: </li></ul><ul><li>-must appreciate the role that probability has in ascertaining the origins of two or more specimens </li></ul><ul><li>Probability: </li></ul><ul><li>-frequency of occurrence of an event </li></ul><ul><li>Exact probability is impossible to define in many analytical processes </li></ul>
  9. 9. Classifying Characteristics <ul><li>Individual Characteristics </li></ul><ul><ul><li>-Evidence associated to a unique source with high degree of probability </li></ul></ul><ul><li>Class Characteristics </li></ul><ul><ul><li>-Evidence associated only with a common source </li></ul></ul>
  10. 10. Individual Characteristics <ul><li>Not possible to state with mathematical exactness the probability that the specimens are of common origin </li></ul><ul><li>-Can only be concluded that this probability is so high as to defy mathematical calculations or human comprehension </li></ul>
  11. 11. Individual Characteristics <ul><li>Examples: </li></ul><ul><ul><li>the matching ridge characteristics of two fingerprints </li></ul></ul><ul><ul><li>random striation markings on bullets/tool marks </li></ul></ul><ul><ul><li>Irregular/random wear patterns in tire/footwear impressions </li></ul></ul><ul><ul><li>handwriting characteristics </li></ul></ul><ul><ul><li>sequentially made plastic bags by striation marks running across the bags </li></ul></ul>
  12. 12. Class Characteristics <ul><li>Frequent inability of the laboratory to relate physical evidence to a common origin with a high degree of certainty </li></ul><ul><li>-class characteristics when it can be associated only with a group and never with a single source </li></ul><ul><li>-probability is a determining factor </li></ul><ul><li>-high diversity of class evidence in our environment makes comparison significant </li></ul>
  13. 13. Class Evidence <ul><li>Weaknesses of forensic science: </li></ul><ul><li>-inability to assign exact/approximate probability values to the comparison of most class physical evidence </li></ul><ul><li>Very few statistical data </li></ul><ul><li>-available from which to derive this information </li></ul><ul><li>-mass-produced world </li></ul>
  14. 14. Class Evidence <ul><li>Primary endeavor: </li></ul><ul><li>-create and update statistical databases </li></ul><ul><li>Most items of physical evidence retrieved at crime scenes cannot be linked definitively to a single person or object </li></ul><ul><li>The value of class physical evidence lies in its ability to provide corroboration of events with data that are, as nearly as possible, free of human error and bias. </li></ul>
  15. 15. Class Evidence <ul><li>Chances are low of encountering two indistinguishable items of physical evidence at a crime scene that actually originated from different sources </li></ul><ul><li>More than one type of class evidence may lead to high certainty that they originated from the same source. </li></ul><ul><li>Contribution of physical evidence is ultimately determined in the courtroom. </li></ul>
  16. 16. Crossing Over <ul><li>How many striations are necessary to individualize a mark to a single tool and no other? </li></ul><ul><ul><li>How many color layers individualize a paint chip to a single car? </li></ul></ul><ul><ul><li>How many ridge characteristics individualize a fingerprint? </li></ul></ul><ul><ul><li>How many handwriting characteristics tie a person to a signature? </li></ul></ul><ul><li>These are all questions that defy simple answers and are the basis of defense lawyer arguments </li></ul>
  17. 17. Natural vs. Evidential Limits <ul><li>Practical limits to properties/characteristics for comparison: </li></ul><ul><ul><li>-Modern analytical techniques are so sophisticated/sensitive that natural variations in objects become almost infinite </li></ul></ul><ul><ul><li>-No two things in this world are alike in every detail </li></ul></ul><ul><ul><li>-Evidential variations are not the same as natural variations </li></ul></ul><ul><ul><li>-Distinguishing variations of evidential use from natural variations is not always an easy task </li></ul></ul>
  18. 18. Using Physical Evidence <ul><li>Number of different objects linking an individual to a crime scene increases: </li></ul><ul><li>-likelihood of that individual’s involvement with the crime </li></ul><ul><li>-exonerated/excluded from suspicion if physical evidence is different from standard/reference samples collected from that subject </li></ul>
  19. 19. Forensic Databases <ul><li>Automated Fingerprint Identification System (IAFIS): </li></ul><ul><li>-fingerprint and criminal history system (FBI) </li></ul><ul><li>Combined DNA Index System (CODIS): </li></ul><ul><li>-electronically exchange and compare DNA profiles </li></ul><ul><li>National Integrated Ballistics Information Network (NIBIN): </li></ul><ul><li>-acquire/digitize/compare markings made by a firearm on bullets and cartridge casings </li></ul><ul><li>International Forensic Automotive Paint Data Query (PDQ): </li></ul><ul><li>-chemical/color information of original automotive paints </li></ul><ul><li>SICAR (shoeprint image capture and retrieval) </li></ul><ul><li>-shoeprint database </li></ul>
  20. 20. Forensic Pathology <ul><li>Forensic Pathology: </li></ul><ul><li>-investigation of unnatural/unexplained/violent deaths </li></ul><ul><li>-Cause and manner of death </li></ul><ul><ul><li>-autopsy </li></ul></ul><ul><ul><li>-toxicology </li></ul></ul>
  21. 21. Forensic Pathology <ul><li>Post Mortem Changes: </li></ul><ul><li>Rigor mortis: </li></ul><ul><li>-stiffening of body parts in position at death </li></ul><ul><li>-early 2-12 hours </li></ul><ul><li>-full 12-24 hours </li></ul><ul><li>-passed 24-48 hours </li></ul><ul><li>Livor mortis: </li></ul><ul><li>-pooling of blood in lowest portion of body </li></ul><ul><li>-blanching (2-12 hours) </li></ul><ul><li>-Fixed (12-24 hours) </li></ul><ul><li>Algor mortis: </li></ul><ul><li>-loss of heat by a body </li></ul><ul><li>-1 to 1 1/2 degrees Fahrenheit per hour until the body reaches the environmental temperature </li></ul>
  22. 22. Beyond the Crime Scene <ul><li>Beyond the crime scene to the autopsy room: </li></ul><ul><li>-medical examiner/coroner </li></ul><ul><li>-tissues/organs for pathological/toxicological examination </li></ul><ul><li>-secure items from the body for laboratory examination </li></ul>
  23. 23. Beyond The Crime Scene <ul><li>The following are to be collected and sent to the forensic laboratory: </li></ul><ul><ul><li>Clothing </li></ul></ul><ul><ul><li>Fingernail scrapings </li></ul></ul><ul><ul><li>Head/pubic hairs </li></ul></ul><ul><ul><li>Blood (DNA/toxicology) </li></ul></ul><ul><ul><li>Vaginal/anal/oral swabs (sex-related crimes) </li></ul></ul><ul><ul><li>Bullets from the body </li></ul></ul><ul><ul><li>Hand swabs (Gunshot Residue) </li></ul></ul>
  24. 24. Forensic Anthropology <ul><li>Identification/examination of human skeletal remains: </li></ul><ul><li>-sex/approximate age/race/skeletal injury </li></ul><ul><li>-create facial reconstructions to identify skeletal remains </li></ul><ul><li>Sites of human remains treated as a crime scene </li></ul><ul><li>-secured and thoroughly searched </li></ul><ul><li>-locate all bones if scattered </li></ul><ul><li>-footwear impressions </li></ul><ul><li>-discarded items </li></ul><ul><li>- aerial photography/metal detectors/ground-penetrating radar/infrared photography/ cadaver dogs </li></ul>
  25. 25. Forensic Entomology <ul><li>Study of insects: </li></ul><ul><li>-estimate the time of death </li></ul><ul><li>-postmortem interval (PMI) </li></ul><ul><li>-different insect species used to estimate PMI </li></ul><ul><li>-all entomological/insect collected </li></ul><ul><li>-temperature readings </li></ul><ul><li>-collect specimens from every area in which they are found </li></ul>