Transcript Estimating Time of Death

Estimating Time of Death
Forensics 2014-1015
Livor Mortis
”Death Color”
• As body begins to decompose blood seeps down through
tissues and settles in lower parts of body
– Red Blood Cells Turn purplish-blue
• Pooling of blood = lividity
• Lividity Begins about 2 hours after death
• Between 2-8 hours lividity will be present, but if the skin is
pressed color will dissappear
• After 8 hours lividity remains if the skin is pressed
• Ambient Temperature = Temperature surrounding body
– affects the rate of lividity
• Higher Temperature = Increase in rate of lividity
• Lower Temperature = Decrease in rate of lividity
Livor Mortis
• What else can be determined from lividity?
– Position of body following death
– Whether a body has been moved post mortem
Algor Mortis
death heat
• The Chill of Death
– Algor Mortis-Describes temperature loss in a corpse
• Rate of loss influenced by environmental conditions
– Exterior temps
– Clothes vs no clothes ect…
– First 12 hours.
• Temperature loss = .78 degrees Celsius (1.4 degrees
Fahrenheit) per hour
– After 12 hours
• Temperature loss = .39 degrees Celsius (.7 degrees
Fahrenheit) per hour
Muscle Fibers and Contraction
Rigor Mortis
“Death Stiffness”
• Normal Muscle Contraction
– Calcium released from membranes inside cell causes muscle fibers cells to
contract
– Active transport then removes calcium so muscle fibers can relax
• This requires oxygen and an energy supply
• The Rigidity of Death
– Stiffness occurs because skeletal muscles are locked in a flexed position and
are unable to relax.
– Calcium leaks out of cell and muscle remains in a contracted position
• No active transport after death
• Starts within 2 hours of death
– Begins with Head (Face) and neck
• Peak Rigor, At 12 hours the body is at its most rigid state
– At about 15 hours muscle fibers break down and soften
• Stiffness gradually disappears after 36 hours
• Rigor may remain for up to 48 hours
Rigor Mortis
Observation
Approx. Time Scale
The body is at its most rigid
state
Just over 2 hours
No visible signs of rigor
Less than 2 hours
or more than 48 hours ago
Stiffness generally
disappears
After 36 hours
Factors Affecting Rate of Rigor
• Ambient Temperature
– Cold- slows rigor
– Warm- Accelerates Rigor
• Clothing or Lack of Clothing
– Clothes = accelerates rigor
– No Clothes = slows rigor
• Sun Exposure
– Accelerates rigor
• Activity/Exercise
– Exercising or struggling = accelerates rigor
– Sleep = slows rigor
• Body Weight
– Obese- slows rigor (fat stores oxygen)
– Thin- Accelerates Rigor
Stomach and Intestinal Contents
• If undigested stomach
contents are present, then
death occurred 0 to 2 hours
after last meal
• If the stomach is empty but
food is found in the small
intestine, then death occurred
at least 4-6 hours after last
meal
• If the small intestines is
empty and wastes are found
in large intestine, then death
probably occurred 12 or more
hours after last meal
Decomposition
• The rotting or break down of all tissues and
organs
– Bacteria and other microorganisms aid the
decomposition process, just as they decompose
plants and animals in the environment.
• Occurs in Predictable Pattern
– Can be used to help determine Time of Death
Stages of Decomposition
• Initial Decay
– Corpse appears normal from the outside, but is starting to
decompose from the actions of bacteria and autolysis
• Putrefecation
– Odor of decaying flesh is present and the corps e appears
swollen
• Black Putrefecation
– Very Strong odor. Parts of the flesh appear black. Gases escape
and the corpse collapses
• Butyric Fermentation
– Corpse is beginning to try out. Most of the flesh is gone
• Dry Decay
– Corpse is almost dry. Further decay is very slow from lack of
moisture
Timeline of Events during
Decomposition
•
•
•
Within 2 days after death:
– Cell Autolysis begins following death
– Green and purplish staining occurs form blood decomposition
– The skin takes on a marbled appearance
– The Face Becomes discolored
After 4 Days:
– The skin blisters
– The abdomen swells with the gas carbon dioxide release by bacteria living in
the intestines
Within 6-10 Days:
– Corpse bloats with carbon dioxide, eventually gas causes the chest and
abdominal cavities to burst and collapse
– Fluids begin to leak from body openings as cell membranes rupture
– Eyeball and other tissues liquefy
– The Skin sloughs off
Factors Affecting Rate of
Decomposition
• Temperature
– Bodies decompose fastest within 21-37 degrees Celsius (70-99
degrees Fahrenheit)
– Below this range rate decreases because cold temperatures
slow the growth of bacteria and microorganisms
– Above this range tends to dry out corpses and preserve them
• Several other factors
–
–
–
–
Illness
Age
Weight
Clothing or Lack of Clothing
Forensic Entomology
• Forensic entomologist
– Collects insect evidence from on, above, and below
the body
– Records environmental conditions
– Because life cycles are affected by fluctuations in the
daily environmental conditions, insects cannot
provide an exact time of death, only a close estimate.
– At crime lab some of the insects are raised under
environmental conditions that mimic the
environmental conditions at the crime scene to obtain
most accurate approximation
Forensic Entomology
• Blowflies are usually the first insects to arrive
at a dead body
– Usually arrive within minutes
• Blowflies exhibit different life stages
– Egg, larva (also known as instars), pupa, prepupa,
adult
Egg
• Soon after Death—blowfly eggs can be found
in the moist, warm areas of a corpse
– < 8 hrs
Larva Stages 1
(Instar 1)
• Within 20 hours
Larva 2
(Instar 2)
• After 2 ½ days
Larva Stage 3
(Instar 3)
• After 4-5 days
Pre-Pupa
• After 8-12 days
Pupa
• After 18-24 days
Adult
• After 21-24 days
Time of Death—Insects
o
The insect life cycle provides scientists with a
benchmark to estimate a time of death
o
Insect evidence cannot provide an exact time of
death—fluctuating environmental conditions
o
Insect evidence provides a close estimate