Forensics: Rigor Mortis

• Forensics Mortis refers to the post-mortem changes that occur in the body after death, which can be used to estimate the time of death (TOD) or post-mortem interval (PMI).

Rigor Mortis

• Rigor mortis is the post-mortem rigidity or stiffening of the body's muscles due to chemical changes in the muscle fibers.
• It is a time-dependent process that can help estimate the time since death.
• The process involves the depletion of adenosine triphosphate (ATP) in muscle cells, which prevents the detachment of myosin cross-bridges from actin filaments, leading to muscle stiffness.
• It typically begins within 2-6 hours after death, starting with the smaller muscles (e.g., eyelids, jaw) and then progressing to the larger muscle groups.
• Rigor mortis usually reaches its full peak at around 12-24 hours after death.
• After the maximum rigor mortis is achieved, the muscles gradually relax as decomposition begins, typically within 24-36 hours after death.
• Several factors can affect the onset, duration, and intensity of rigor mortis, including the ambient temperature, the individual's age, physical activity before death, and body condition.
• Higher temperatures accelerate rigor mortis, while lower temperatures delay it.
• Individuals who were physically active before death may experience a faster onset of rigor mortis.
• In forensic investigations, the presence, distribution, and degree of rigor mortis are carefully assessed to estimate the time since death.

Algor Mortis

• Algor mortis refers to the cooling of the body after death until it reaches ambient temperature.
• It is a crucial parameter used in estimating the post-mortem interval (PMI).
• The rate of cooling depends on various factors, including ambient temperature, body size, clothing, and environmental conditions.
• Glaister's equation is a formula used to approximate time since death based on body temperature: Hours since death = (98.4°F - rectal temperature) / 1.5
• Glaister's equation assumes an average body temperature of 98.4°F (36.8°C) and a constant cooling rate of 1.5°F per hour.
• The cooling rate is not constant and is influenced by several factors
• The Stark-Henssge nomogram is another tool used to estimate time since death based on body temperature, body weight, and ambient temperature.
• It provides a more accurate estimation than Glaister's equation by considering multiple variables.
• Factors affecting algor mortis include:
  • Ambient temperature significantly impacts the rate of cooling; warmer environments slow cooling, while colder environments accelerate it.
  • Body size and composition influence heat loss; larger individuals cool more slowly than smaller ones due to a smaller surface area-to-volume ratio.
  • Clothing insulates the body, slowing down heat loss; the type and amount of clothing can affect the cooling rate.
  • Air movement increases heat loss through convection; windy conditions accelerate cooling.
  • Immersion in water enhances heat loss due to water's high thermal conductivity, leading to faster cooling compared to air.
  • Illness and medications: Fever or certain drugs can affect the initial body temperature and cooling rate.
• Forensic investigators measure the body's core temperature, usually rectally, and consider these factors to estimate the time since death.
• Algor mortis is most accurate within the first 24 hours after death.

Livor Mortis

• Livor mortis, also known as post-mortem lividity or hypostasis, is the discoloration of the skin after death due to the settling of blood in the dependent parts of the body.
• After death, circulation ceases, and gravity causes blood to accumulate in the capillaries and small vessels of the lower parts of the body.
• The affected areas appear purplish or reddish-blue.
• Livor mortis typically begins within 30 minutes to 2 hours after death and becomes fixed within 8-12 hours.
• The pattern and intensity of livor mortis can provide information about the position of the body after death and whether the body has been moved.
• If the body is moved within the first few hours after death, livor mortis may shift to reflect the new position.
• However, once livor mortis is fixed, the discoloration will not change, even if the body is repositioned.
• Factors affecting livor mortis include:
  • The amount of blood in the body affects the intensity of livor mortis; individuals with anemia may have less pronounced lividity.
  • The position of the body greatly influences the distribution of livor mortis; areas in contact with a surface may show blanching due to compressed capillaries.
  • The time since death determines whether livor mortis is fixed or unfixed; unfixed lividity will shift with changes in body position.
  • The cause of death can influence the color of livor mortis; carbon monoxide poisoning may result in a cherry-red discoloration.
• Forensic investigators examine the distribution, color, and intensity of livor mortis to help determine the time of death and whether the body has been moved.
• Pressure from clothing or other objects can prevent the settling of blood in those areas, resulting in a lighter color, known as blanching.

Rigor mortis is the post-mortem rigidity of muscles. It helps estimate time since death. ATP depletion prevents muscle detachment, causing stiffness that starts in smaller muscles.