Estimating Time of Death
6.1 Understand how to determine the time of death of a mammal by examining the extent of
decomposition, stage of succession, forensic entomology, body temperature and degree of muscle
contraction.
Post-Mortem Stages of Death
1. Pallor Mortis – Paleness of the Skin
2. Algor Mortis – Cooling of the Body
3. Rigor Mortis – Stiffening of Body Muscles
4. Livor Mortis – Settling of the Blood
Body Temperature
• All mammals produce heat from metabolic reactions, e.g. respiration.
• The human body has a core body temperature of around 37°C.
• From the time of death, metabolic reactions slow down and eventually stop, causing the body
temperature to fall until it equals the ambient temperature (algor mortis).
• Core body temperature decreases in a stereotypical way, so forensic scientists can estimate the time
of death based on how much the body has cooled.
• Various conditions may increase the rate of cooling of the body:
o Body Size – higher surface area: volume ratio.
o Body Position – higher surface area exposed to air.
o Clothing – more (insulating) clothing.
o Air Movement – greater air movement.
o Humidity – higher humidity.
o Injury – greater extent of injury.
o Ambient Temperature – lower ambient temperature relative to body.
Degree of Muscle Contraction
• After death, the muscles in the body start to contract and become stiff (rigor mortis).
1. Anaerobic respiration still occurs, causing a build-up of lactic acid.
2. This decreases the pH of the cells, inhibiting the enzymes that produce ATP.
3. Without ATP, the bonds between the myosin and actin in the muscle cells become fixed.
• Rigor mortis only lasts for a few hours.
• Decomposition by the action of bacteria/fungi break down the biological molecules, including actin
and myosin.
• Sarcomeres and muscle fibres deteriorate, softening muscle tissue.
• There is a progression in the development of rigor mortis, with smaller muscles stiffening before
larger ones.
• Rigor mortis will set in more quickly an last for a shorter period of time if:
o The environmental temperature is high.
o The person had been physically active before death.
3
6.1 Understand how to determine the time of death of a mammal by examining the extent of
decomposition, stage of succession, forensic entomology, body temperature and degree of muscle
contraction.
Post-Mortem Stages of Death
1. Pallor Mortis – Paleness of the Skin
2. Algor Mortis – Cooling of the Body
3. Rigor Mortis – Stiffening of Body Muscles
4. Livor Mortis – Settling of the Blood
Body Temperature
• All mammals produce heat from metabolic reactions, e.g. respiration.
• The human body has a core body temperature of around 37°C.
• From the time of death, metabolic reactions slow down and eventually stop, causing the body
temperature to fall until it equals the ambient temperature (algor mortis).
• Core body temperature decreases in a stereotypical way, so forensic scientists can estimate the time
of death based on how much the body has cooled.
• Various conditions may increase the rate of cooling of the body:
o Body Size – higher surface area: volume ratio.
o Body Position – higher surface area exposed to air.
o Clothing – more (insulating) clothing.
o Air Movement – greater air movement.
o Humidity – higher humidity.
o Injury – greater extent of injury.
o Ambient Temperature – lower ambient temperature relative to body.
Degree of Muscle Contraction
• After death, the muscles in the body start to contract and become stiff (rigor mortis).
1. Anaerobic respiration still occurs, causing a build-up of lactic acid.
2. This decreases the pH of the cells, inhibiting the enzymes that produce ATP.
3. Without ATP, the bonds between the myosin and actin in the muscle cells become fixed.
• Rigor mortis only lasts for a few hours.
• Decomposition by the action of bacteria/fungi break down the biological molecules, including actin
and myosin.
• Sarcomeres and muscle fibres deteriorate, softening muscle tissue.
• There is a progression in the development of rigor mortis, with smaller muscles stiffening before
larger ones.
• Rigor mortis will set in more quickly an last for a shorter period of time if:
o The environmental temperature is high.
o The person had been physically active before death.
3
