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Forensic Science

Forensic Science

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Forensic Science

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  1. Forensic Science Forensic Biology Time of Death

  2. Forensic File #1 • What are 2 important things that microorganisms like diatoms, algae, and/or other protists can tell a forensic scientist?

  3. What happens once a body is found? • Medical examiner or coroner must pronounce the person “dead” • Photographs are taken of body “in situ”- in position found • Any physical evidence around body is photographed and collected • Body may be rearranged, clothes searched for ID, some evidence obtained at scene (skin swabs for trace evidence) • Medical examiner may try to determine manner of death at scene- to determine if body needs to be taken to the morgue or if it can be released to funeral home

  4. Identify manner, cause, mechanism of death • Manner of death: Accident, homicide, natural, suicide, undetermined • Cause of death: bleeding out, heart failure, brain death, asphyxiation • Mechanism of death: what causes the “cause”

  5. Example: • A man dies from a stab wound to the abdomen that he obtained during a fight with another person. • Manner- homicide • Cause- bleeding out • Mechanism- knife wound

  6. Determination of time of death • Time of death is important to investigators because it can establish when crime occurred- check alibis of suspects, know when to question witnesses, etc. • Utilize: livor mortis, rigor mortis, algor mortis and insect activity to determine time of death or PMI (post mortem interval)

  7. What is livor mortis? • Means “death color” • Blood pools at the lowest point of the body once heart stops beating • Lividity begins about 2 hours after death • Discoloration becomes permanent after 8 hours • Influenced by temperature- faster when warmer Discoloration is on back of body- indicates body was face up

  8. What is rigor mortis? • Means “death stiffness” • Starts within 2hours of death • Starts with head & moves down body • Stiffness occurs because the skeletal muscles are unable to relax and remain contracted & hard • These changes occur due to chemical changes that occur after death

  9. What affects rigor? • Ambient temperature • Person’s weight • Type of clothing • Illness • Level of physical activity prior to death • Sun exposure • Essentially- the warmer the person was at death, faster rigor occurs

  10. Progression of Rigor

  11. What is algor mortis? • Means “death heat” • Describes temperature loss that occurs after death • Temperature taken with thermometer inserted into the liver to get a “core temperature”

  12. Today’s assignments • Due today: Microbe Murder Mystery lab • Today’s assignment: Time of Death packet on front table

  13. Time of Death- • Day Two • Make sure your name is on your Time of Death packet

  14. Forensic File #2 This body was found at the scene face down and the lead investigator immediately knew that the body had been moved. How did he know?

  15. Other methods to determine time of death

  16. Why look at stomach and intestinal contents? • 4 to 6 hours for the stomach to empty its contents • Another 12 hours for food to leave small intestine • takes approximately 24 hours after the meal until undigested food is released

  17. What changes in the eye after death? • Surface of eye dries out • Thin film is observed within 2 to 3 hours after death

  18. What are the stages of decomposition? • After 2 days: cell autolysis; green/purplish staining; skin marbles; face becomes discolored • After 4 days: skin blisters; abdomen swells • Within 6 to 10 days: corpse bloats/splits; fluids begin to leak; eyeballs/tissues liquefy; skin sloughs off

  19. Stages of decomposition

  20. Evidence of physical trauma Appearance and extent of injuries depend on: • Amount of force • Weapon’s surface area and mass • Part of body affected Force= mass x acceleration Pressure= force/surface area

  21. Types of trauma • Blunt-force trauma- victim is hit by something hard, or falls onto a hard object • Blunt force trauma is divided into three categories: • Abrasions • Contusions • lacerations

  22. Abrasions • When portion of the skin has been removed • Brush abrasions- force applied parallel to skin (brush, scrape) skin damaged in direction of the force • Impact abrasions- force applied perpendicular to the skin

  23. Contusions • Also known as a bruise • Trauma caused by broken blood vessels • May be large enough to cause swelling- hematoma

  24. Laceration • Tear in the tissue caused by sliding or crushing force • Extreme force involved

  25. Sharp-force trauma • Four categories • Stab wounds • Incised wounds • Chop wounds • Therapeutic wounds

  26. Stab wounds • Typically deeper than it is wide • Penetrating wounds- result in punctured organs • Perforating wounds- puncture an organ and come out the other side

  27. Incised wounds • Longer than it is deep • Usually center is deepest • Not typically fatal

  28. Chop wounds • Heavy tools • Incised wounds with deep internal injuries

  29. Therapeutic wound • Produced by surgery

  30. Today’s agenda: • Due today- Time of death packet • Today’s work: BOTH on front table • Diagramming injuries • Applying directional terms