Time of Death

Question 1

Name techniques to determine time of death

Answer 1

Body temperature, rigor mortis, decomposition, forensic emotology

Question 2

Describe how body temperature changes after death

Answer 2

Begins at 37°C, S-shaped curve
- initial plateau lasts 30-60 mins, body then quickly cools to room temperature
- After 24 hours body usually finishes cooling and temperature is no longer useful

Question 3

How is body temperature of a corpse measured?

Answer 3

• using a long thermometer with a wide range
• usually taken rectally or using abdominal stab

Question 4

How do some factors affect post-mortem cooling?

Answer 4

Size of body —> SA:V determines heat loss, faster for smaller organisms
ambient temperature —> heat loss to air slower than water, water conducts heat better
body position —> if body compact, cooling is slower
clothing —> provided insulation
humidity + air movement —> less heat loss in more humid environment, air movements speed up cooling

Question 5

Why does decomposition occur?

Answer 5

• Autolysis = breakdown of body tissues using body’s enzymes from digestive system + lysosomes
• Bacteria from the gut invade tissues + release more enzymes –> tends to happen in anaerobic restoration, as it favours anaerobic bacteria

Question 6

What are signs of decomposition?

Answer 6

• Skin discolouration - greenish colour develops in lower abdomen (due to formation of sulphaemoglobin in blood) spreads to remainder of body, darkens to reddish-green and finally purple-black over 36-72 hrs
• Body bloating
• Gas and liquid filled blisters under skin due to action of bacteria where gases (hydrogen sulphide, methane, CO2, H) build up in intestines and tissues
• At later stages gas releases and body deflated, when fluid drains, tissue shrink

Question 7

What is rigor mortis?

Answer 7

3. Joints becoming fixed in their position at tod, relaxing then stiffening after death

Question 8

Describe stages of rigor mortis

Answer 8

• after death muscle cells become starved of oxygen and O dependent reactions stop
• respiration in cells become anaeroboc producing lactic acid
• pH of cells fall, inhibiting enzymes, thus inhibiting anaerobic reactions
• ATP needed for muscle contraction no longer produced, so bonds between muscle proteins fix
• Proteins can no longer move each other to shorten muscle and joints

Question 9

How can body temp and stiffness determine TOD?

Answer 9

Warm and not stiff = no longer than 3 hrs
Warm and stiff = dead 3-8 hrs
Cold and stiff = dead 8-36hrs
Cold and not stiff = dead more than 36-48 hrs

Question 10

What is forensic entomology?

Answer 10

Use of insects to help scientists determine TOD

Question 11

Describe insect succession

Answer 11

1) Colonisers—> anaerobic bacteria from gut spread over body causing decomp
2) Pioneers —> blowflies lay eggs/feed on decomposing tissue; makes body favourable for beetles
- body dries out, less favourable for flies do they leave and beetles remain
3) Beetles —> eat maggots; only leave when no tissue left on body
4) Parasitic wasps —> lay eggs in fly/beetle larvae

Question 12

How can entomology help determine TOD?

Answer 12

• blowflies lay eggs in corpse within few hours
• maggots hatch ~24 hours later and feed on body until pupa forms
• maggots cause liquification of tissue
  which adult flies feed on
• based on life stage of blowflies we can determine TOD

Question 13

When does rigor mortis occur?

Answer 13

4-6 hours after death