1. Forensic Biology Time of Death
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 Time after death Event Appearance Circumstances
2 to 6 hours
Rigor begins
Body becomes stiff & stiffness moves down body
Begins with eyelids & jaw, then center, then extremities
12 hours
Rigor complete
Peak rigor is exhibited
Entire body is rigid
15 to 36 hours
Slow loss of rigor
Loss of rigor in small muscles first then large
Lost first in head & neck; last in bigger leg muscles
36 to 48 hours
Rigor totally disappears
Muscles become relaxed
Many variables may extend 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
What happens
Initial decay
Normal on outside; starting to decompose
Putrefaction
Odor of decay present; corpse swollen
Black putrefaction
Very strong odor; flesh appears black; gases escape & corpse collapses
Butyric fermentation
Corpse is beginning to dry out; most of flesh is gone
Dry decay
Corpse is almost dry

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