Estimating Time of Death

Forensics 2013-1014

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

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

The body is at its most rigid state

No visible signs of rigor

Stiffness generally disappears

Approx. Time Scale

Just over 2 hours

Less than 2 hours or more than 48 hours ago

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

Algor Mortisdeath heat

• The Chill of Death– Algor Mortis-Describes temperature loss in a

corpse– 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

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