Rior Mortis : Methods of Estimation of Time Since Death (TSD)

Rior Mortis : Methods of Estimation of Time Since Death (TSD)

There is no known legal definition of death. From a medical or biological point of view, Death is characterized by an irreversible & permanent loss of vital functions which causes cessation of life. Following an individual’s death, there is a certain specific sequence of events that occur in the body as a part of a natural phenomenon, which ensures that the body is decomposed and restored to the earth. Thus, we can say that “Death is a part of life, and decomposition is a part of death.”

The term “Post-Mortem” is used to refer to the ‘events that occur after Death’. Similarly, ‘Post-mortem changes’ refers to the changes that occur in the body after an individual dies. This is when Forensic Medicine comes into the picture, where it plays an important role in determining an individual’s manner of death, especially in the cases where the person has died under suspicious circumstances. 

 “Forensic Thanatology is also known as ‘the scientific study of death’. This is an area of Forensic Medicine that investigates the mechanisms and forensic aspects related to death, which include the bodily changes that accompany death and the post-mortem period.

The elements related to the death of a person are analysed as diligently as possible in order to state whether they died of natural causes or due to an external factor. The most common opinion among specialists, encompassed in a list of situations which are unequivocally associated with death, places Rigor Mortis alongside decapitation, decomposition, and massive cranial/cerebral destruction, which are all elements that easily establish the death of a person (Lockey, 2002). Consequently, the phenomenon of Rigor Mortis is indisputable proof for a person to be considered deceased.

Once death is confirmed, the process of measuring the interval in which it may have occurred begins. After the assessment of the first signs of death, the Rigor Mortis stage will act as an additional clue when estimating the time of death. Contrary to Algor Mortis, this stage has neither the same reliability, nor is it first in the assessment hierarchy. Besides not having the formula to calculate how much time has passed since its onset, it can only affect the time frame previously provided by other measurement tools. Even so, Rigor Mortis must be taken into account because due to the fact that it preserves the last position of the body, it contributes to the reconstruction of the events which led to the person’s death. Multiple conclusions can be drawn based on the stages of development of Rigor Mortis in a particular case.

There are two methods for estimating the time of death:

1. The rate method. Measuring the change produced by a process which takes place at a known rate which was either initiated or stopped by the event under investigation, i.e. death. Examples include the amount and distribution of rigor mortis, the change in body temperature, and the degree of putrefaction of the body.

2. The concurrence method. Comparing the occurrence of events which took place at known times with the time of occurrence of the event under investigation, i.e. death. For example, a wrist watch stopped by a blow during an assault, the extent of digestion of the last known meal.

Once the death sets in, the body falls motionless and a gradual release of muscular tension will follow (Pounder, 2018) since physical movement is unable to continue beyond the cessation of vital functions. This flaccid state will be present in all muscles and it will take anywhere between three-six hours for it to be complete, before being replaced by post-mortem rigidity or Rigor Mortis (Swift, 2006). However, this hardening process eventually diminishes, so it will not be long until the muscles will relax again.

Rigor mortis (Latin: Rigor – stiffness, mortis – of death) stands for the stiffening of the muscles as a reaction occurring after death, due to a physico-chemical process that takes place internally. In a nutshell, the muscles are imitating a pre-mortem normal contraction which spans over a longer period of time, supported by the post-mortem loss of integrity, without being followed by a corresponding body movement (Pounder, 2018). Externally, the body will remain frozen in the last position adopted after the events which led to that person’s death. Newton’s law encounters a ground for application here as well, since post-mortem rigidity cannot set the body in a position that defies gravity or the surrounding objects (Pounder, 2018).

A peculiar aspect that may sometimes overlap with Rigor Mortis would be the cadaveric spasm, which is an instantaneous local muscular contraction. In spite of its rare occurrence, it is most often linked with violent deaths (Pounder, 2018) and unlike the second stage of human decay, the contraction is persistent and is released only when the muscles begin to be destroyed by the process of decomposition .

The Importance of the Time of Death

An accurate estimation of the time of death can lead to discovering the identity of the assailant. In criminal cases, it can eliminate some suspects while focusing attention on others. For example, a husband says that he left for a business meeting at 2 P.M. and returned at 8 P.M. to find his wife dead. He says that he was home all morning and that she was alive and well when he left. If the ME determines the time of death was between 10 A.M. and noon, the husband has a great deal of explaining to do. On the other hand, if the estimation reveals that the death occurred between 4 and 6 P.M., and the husband has a reliable alibi for that time period, the investigation will move in a different direction.

Notice that in the above example the ME gave a range rather than an exact time for his estimated time of death. He didn’t say 4:30 P.M. but rather said between 4 and 6 P.M. Simply put, that’s the best he can do and that’s why it’s called the estimated time of death. It’s a best guess.

The time of death is not confined to criminal investigations; it can also come into play in civil situations. Insurance payments may depend upon whether the insured individual were alive at the time the policy went into effect or if he died before the policy expired. Even a single day can be important. Likewise, property inheritance can hinge on when the deceased actually died. Suppose two business partners die near the same time. Their contract may read that the company assets go the survivor if one of them dies. In this case, the heirs of the one that died last would own the company assets. Similarly, the dispersal of property under a will might be affected by which partner died first.

Methods of Estimation of Time Since Death (TSD)

The early post-mortem phase is probably the most important time period for PMI estimation, as most medico-legal cases are examined in this time period. This period is also where the estimation of time since death is most relevant in establishing the timeline of events and developing a theory of circumstances of death. This period runs from 3 to 72 hours after death. The early post-mortem phase is most frequently estimated using the classical triad of post-mortem changes – rigor mortis, livor mortis, and algor mortis.

Algor Mortis

Algor mortis is the cooling of the body after death, primarily due to the loss of homeostatic regulation by the hypothalamus, in conjunction with the loss of heat to the environment by conduction, convection, and radiation. Algor mortis is the most accurate method of estimating TSD in the early post-mortem phase. However, it involves a cumbersome procedure and requires intensive knowledge and research before it is accurately usable in the field; this is due to the numerous factors that affect the temperature gradient between body temperature and ambient temperature, the most inherent being the differences in the temperatures of different localities at different points of time. A rule of thumb states that there is a decrease of 1.5 degrees F every hour. Several charts, formulae, and algorithms have been developed to estimate the PMI, Henssge’s nomogram being the most widely taught. The estimation of TSD using algor mortis measures rectal temperatures. While they have been consistently used, nomograms for brain temperatures have also been developed by Brinkmann et al. in 1976 and 1978 and by Henssge et al. in 1984.

Cooling of the body or Algor mortis 

It is seen within 15 minutes after death. In this the body core  temperature (BCT) decreases. Thanatometer is a chemical thermometer used to measure BCT in  post-mortem. It may be 25-30 cm. It can measure temperatures between 0-50°C. Ideal site for recording temperature is the rectum (rectal temperature is almost equal to BCT).

Other sites include the inferior surface of the liver, external auditory meatus, nasal spaces, and the lower end of the esophagus. Graph illustrating the relationship between temperature and time post-mortem produces a sigmoid curve or inverted S-shape curve.

• Stage I: Isothermic phase.
• Stage II: Steep decline.
• Stage III: Gradual decrease.

Algor mortis  Occurs in 3 phases 

• 1sr phase: Gradual decrease in BCT
•  2nd phase: Rapid decrease in BCT
•  3rd  phase: Gradual decrease in BCT · Shape of Algor mortis curve is Sigmoid.

Rate of fall of temperature is 0.4°C – 0.7°C / hr that is, in summer it is  0.4° C / hr and in winter it is 0.7° C / hr. Average fall of temperature  is 0.5 C/hr. By knowing the rate of fall, we can calculate time since death.

Post-Mortem Caloricity 

Normally, the body becomes cold within 15 mins after death [Algor mortis]· But, if the body remains warm for 1-2 hrs even after death, it is known as  Post-mortem caloricity. Whenever there is increased body core temperature  at the time of death, post mortem caloricity is seen.

Increased body core temperature at death is seen in  conditions with increased Muscle contraction that is Tetanus, Strychnos Nux vomica poisoning exercises etc. Defective thermoregulation in the body is associated with Heat stroke, Pontine hemorrhage [have pyrexia, paralysis, pinpoint pupils] and  Septicemia.

Rigor Mortis

Rigor mortis is the post-mortem stiffening of muscles caused by the depletion of adenosine triphosphate (ATP) from the muscles, which is necessary for the breakdown of actin-myosin filaments in the muscle fibers. Actin and myosin are components of the muscle fiber and form a bond during contraction. The cessation of oxygen supply causes the stoppage of aerobic respiration in the cells and leads to a lack of ATP production. Rigor mortis starts immediately after death and is usually seen in a sequence known as the “march of rigor” and Nysten’s Law. While rigor mortis develops simultaneously in all muscle tissue in the body, voluntary and involuntary, the size of the muscle determines the perceptibility of changes by the examiner. Smaller muscles over the face – around the eyes, around the mouth, etc. are the muscles where rigor mortis first appears, followed by rigor mortis of the muscles in the hands and upper limbs, and finally appears in the large muscles of the lower limbs. Rigor mortis appears approximately 2 hours after death in the muscles of the face, progresses to the limbs over the next few hours, completing between 6 to 8 hours after death.Rigor mortis then stays for another 12 hours (till 24 hours after death) and then disappears. In the last phase of rigor mortis, the actin-myosin complex that has formed starts disintegrating due to proteolysis, resulting in the dissolution of the stiffness. This process begins in all the cells at the same time. However, just like with the appearance, this change is perceptible first in the smaller muscles of the face, followed by muscles of the upper limbs, and finally, the large muscles in the lower limbs. Rigor mortis generally disappears 36 hours after death, followed by a phase known as secondary flaccidity.

Rigor mortis or postmortem rigidity refers to the stiffness of the muscles and joints of the body after the death of an individual, which normally endures between one to four days. It is the third stage and an observable indication of death that occurs because of the chemical changes in the muscles that realize a stiffening of the muscles of limbs.

Rigor mortis is one of the most well-known taphonomic alterations, and it is the process by which the body’s muscles stiffen, resulting in rigidity, as a result of a variety of chemical changes in the muscle structure. Rigor mortis is one of the conspicuous taphonomic changes that causes rigidity in the structure of muscles. The event and physiology of rigor mortis are imperative to comprehension. In this article, we will learn about rigor mortis, what is rigor mortis, the causes of rigor mortis, the different stages of rigor mortis, and the occurrence of rigor mortis.

Causes of Rigor Mortis 

The conversion of ATP to ADP is required by muscle fibers, which move in life due to the sliding filament theory. After death, when respiration stops, the intracellular pH drops as lactic and pyruvic acid are produced. Glycogen depletion and hence lower ATP concentrations are caused by the anaerobic metabolism of glycogen in the muscles. Calcium also leaks into the sarcomere, where actin and myosin protein filaments are arranged in an alternating pattern, where calcium binds, allowing cross-linking to occur between the filaments. This generates a pulling motion along the muscle’s length, making it shorter and stiffer.

The causes of rigor mortis are clarified in detail below: 

1. Chemical changes

Chemical changes in the muscles after death bring about rigor mortis. At the point when an individual bites the dust, the body no longer gets oxygen. Subsequently, chemical reactions and trades don’t happen. The muscles can’t create ATP. The actin and myosin filaments stay contracted and the muscles stay tense.

2. Temperature

The body of an individual who died in a hotter atmosphere will encounter chemical changes quicker than that in a colder atmosphere. The bodies lowered in freezing water for a few days don’t experience phases of rigor mortis. It just starts once the body begins to defrost.

Physical changes

The muscles become tight in rigor mortis as a result of this. All of the body’s muscles are harmed. Rigor mortis starts with the eyelids, neck, and jaw and lasts for two to six hours after death. The sequence could be due to lactic acid levels differing amongst muscles, which is linked to glycogen levels and muscle fiber types.

Within the next four to six hours, rigor mortis spreads to additional muscles, including internal organs. The age, sex, physical condition, and muscle build of a person can all influence the onset of rigor mortis. Rigor mortis usually peaks after 12 hours and fades after 48. Because of their lesser muscular mass, rigor mortis may be undetectable in many newborn and child bodies.

Occurrence of Rigor Mortis 

1. The sliding fiber hypothesis in strands of muscles relies on the conversion of ATP to ADP.
2. Post-death, because of the absence of respiratory action in the corpse, there is a sensational reduction in the pH level of the cells because of the amalgamation of pyruvic and lactic corrosive.
3. The glycolysis of glycogen without oxygen in muscles causes glycogen exhaustion prompting fewer ATP concentrations where ATP would somehow or another be utilized to isolate the cross-connecting of filaments. Thus the related rigidity would be switched.
4. This rigidity is first seen in quite a while focused at littler muscle bunches that reach out from a range of 4 hours, inevitably moving toward bigger muscle classes inside 12 hours post-death bringing about the body getting stiffened.
5. It relies on diminished degrees of ATP at the hour of death.
6. Rigor Mortis discovers applications in the reconstruction of the postmortem time frame by keeping up the specific position of the body, showing any endeavors made to move the corpse that depends upon – rigidity of the body at the hour of its revelation and the time factor.
7. The body turns around to a floppy state following 36-40 hours from the hour of death.
8. During death, essential flabbiness happens causing stiffening of the muscles of jaws, eyelids, neck.

Stages of Rigor Mortis 

There are four significant stages of rigor mortis namely, autolysis, bloat, active decay, and skeletonization. All these rigor mortis stages are clarified in detail:

Stage I: Autolysis

This stage is otherwise called self-digestion and starts following death. The blood circulation and respiratory exercises stop not long after death. The body can’t get oxygen or evacuate metabolic waste. This makes an acidic environment in the body because of that the cells burst. Little rankles begin showing up on the skin and inside organs. The top layer of the skin starts to relax. The membranes produce enzymes that eat the cells.

Stage II: Bloat

The enzymes delivered by the membranes produce numerous gases. The shade of the skin blurs because of the sulfur-containing mixes discharged by the bacteria. Foul smells are delivered by the microorganisms in the process called putrefaction.

Stage III: Active Decay

All the body parts become liquified at this stage. All the delicate tissues of the body decay. The leakage of fluids through orifices signals the start of active degradation. The organs, muscles, and skin liquefy. Hair, bones, cartilage, and other decay byproducts remain after all of the body’s soft tissue has decomposed. During this period, the cadaver loses the most weight.

Stage IV: Skeletonization

There is no set time span when skeletonization happens. This is on the grounds that the decomposition rate relies on the loss of organic and inorganic components. Skeletonization refers to the final stage of decomposition when the soft tissues of a body or carcass have deteriorated or dried to the point where the skeleton can be seen.

For a long time, rigor mortis has been employed to determine the period since the death. It is regarded as the most essential and fascinating way for calculating the time since death.

Understanding the process of rigor mortis

Muscles need energy to function, in the form of adenosine triphosphate. Our muscles are made of two protein bands called myosin and actin, which move toward one another, contracting the muscle. Energy is then needed to let the bands separate from one another, relaxing the muscle.

Following death, the muscles become weak because the brain cannot tell the muscles to contract or relax. The muscles still have energy reserves that can be used, so the muscles stay relaxed. After a few hours, this energy reserve starts to drain until it is completely depleted. Without any respiration activity or food consumption, no ATP is produced. Hence, the muscles freeze in the position they are in. Although this begins to affect the entire body simultaneously, the smaller muscles such as those in the eyelids, face, and fingers turn stiff first.

What are the stages of death?

• Pallor mortis: The main change that occurs is increased paleness because of the suspension of blood circulation. This is the first sign and occurs quickly, within 15-30 minutes of death.
• Algor mortis: Humans are warm-blooded creatures, which means that we keep a consistent body temperature, regardless of the external environment. The brain is our temperature regulator, and the circulatory framework is the principal heat dissipator. After death, the brain cells stop signaling, and the heart stops pumping blood, which means the body begins to match the external temperature. Our normal body temperature level is 98.6°F (37°C). Assuming the surrounding temperature around the dead body is not exactly the same, it normally takes somewhere in the range of 18-20 hours for the body’s temperature to match the external temperature.
• Rigor mortis: Following death, the body will turn stiff. The muscles become loose and limp, yet the entire body will stiffen after a couple of hours.
• Livor mortis: This is the last phase of death. When the heart stops pumping, the blood is pulled by gravity and begins to collect in certain areas depending on the position of the body. Lividity begins with the skin where the blood has settled, giving it a bright red tone. After a few hours, the color changes from red to blue or purple. This can take about 6-8 hours.
• Decomposition: This stage includes two distinct cycles: autolysis and putrefaction. Autolysis starts when the cells start to release enzymes and goes on for about 2 hours after cells starved of oxygen die and lose their structure. After autolysis comes putrefaction where the dead body becomes bloated and decays, and dry phases of decomposition begin. Bacteria inside the body produce gases that the non-breathing corpse can’t diffuse. The eyes and tongue might protrude and begin to smell of death. Bloating normally starts around the second day of postmortem and proceeds to last for 5-6 days.

Factors That Affect Rigor Mortis

Temperature is the primary factor influencing when rigor mortis begins and ends, but there are other considerations:

• Temperature: Warmer temperature speed the pace of rigor mortis.
• Physical Exertion: If a body engages in strenuous exercise prior to death, rigor mortis may set in immediately. This is because exertion uses oxygen and ATP.
• Age: Rigor mortis occurs more rapidly in the very young and very old because they have lower muscle mass.
• Illness: Illness is another physiological stress that leads to a rapid onset of rigor mortis.
• Body fat: Fat insulates the body, slowing the rate of rigor mortis.

Rule of 12

• In the first 12 hours after death, rigor mortis appears in all body muscles.
• In the next 12 hours, it persists in all body muscles.
• In the next 12 hours, it disappears from all body muscles.
• Rigor mortis appears and disappears within 36-48 hours after death, thereby aiding in the determination of TSD.

Time since death: …. Changes observed

1-2 hours: ………Early signs of lividity.

2-5 hours: ………Clear signs of lividity throughout body. Fixed in 6-10 hours

5-7 hours: ………Rigor mortis begins in face.

8-12 hours: …….Rigor mortis established throughout the body, extending to arms and legs

12 hours: ……….Body has cooled to about 25°C internally.

20-24 hours: …..Body has cooled to surrounding temperature.

24 hours: ……….Rigor mortis begins to disappear from the body in  roughly the same order as it appeared.

36 hours: ……….Rigor mortis has completely disappeared.

48 hours: ……….Body discoloration shows that decomposition is beginning.

Why do the muscles stiffen?

Our muscles are made up of densely packed muscle fibres known as “Myofibrils” which extends throughout the length of the muscle. These myofibrils are made up of two protein filaments named, “Actin” and “Myosin”. Under the influence of a nerve signal, our muscles contract as a result of the interlocking of actin and myosin protein filaments. The muscles continue to remain contracted until there is a sufficient level of ATP in the muscle to enable the detachment of the cross-linking fibres. 

However, once the molecular death begins, the cells begin to die as a result of the lack of oxygen in the body, which stops the biochemical reactions and exchanges that are required for muscle relaxation. 

Bodily changes after death:

As mentioned earlier, following our death, several changes occur in our body. This occurs as a result of complex physicochemical activities occurring in the body as well as the external environmental factors that affect the body. These bodily changes occur in an orderly manner, and this is what helps the forensic investigators to estimate the time since death (Post-mortem Interval).

Stages of Death:

In a biological sense, death is said to occur in two stages. The first being the “Somatic Death”, which is also known as “Systemic Death”. This is followed by the second stage, which is called as the “Molecular Death” or “Cellular Death”. (Reddy & Murty, 2014)

The signs of death appear in the order as stated below.

1. Somatic Death (Systemic Death):

• This characterized by the complete and irreversible loss of vital functions of the body. This includes the cessation of the Heart, Lungs and the Brain. These three vital organs together are known as the “Bishop’s Tripod of Life”.
• Somatic death can be tested by the withdrawal of any artificial life support systems such the ventilator, artificial pacemakers, internal defibrillators, dialysis machines, etc.
• It must be understood that it takes some time for the vital organs to completely cease functioning. Therefore, at this stage, the cells and tissues in the body are still alive.

2. Molecular Death (Cellular Death): 

• During this stage, sequential death of the cells and tissues in our body occurs.
• This stage starts 1-2 hours after the cessation of the function of the vital organs.
• The cells begin to die as the anaerobic processes stop, due to the non-availability of Adenosine Triphosphate (ATP), which acts as the main source of energy for most cellular processes.

Signs of Immediate Post- Mortem Interval (PMI) in the body 

Once the stage of molecular death begins, there will be visible changes on the external surface of the body. These can be observed as changes that appear on the skin, eyes and muscles.

1) Changes in the Skin: 

Within a few minutes after death, the skin begins to lose its elasticity. In addition to this, their skin tends to become pale and ashy in appearance. The lips begin to lose moisture and slightly harden, giving it a brownish and dry appearance.

2) Changes in the Eye:

Some of the changes in the eyes may be observed as the following:

• Opacity or Cloudiness of the Cornea
• Loss of reflex of the Pupils and Cornea: which is checked by using a torch or other light source. If the Pupils do not constrict, it indicates that it has lost its reflex. The pupils will remain dilated.
• Flaccidity of the Eyeball: The eyelids become droopy and the eyeball sinks into the eye socket.
• At a biochemical level, a steady rise in potassium level in the vitreous humour is seen, which can be detected up to 100 hours after an individual’s death.

3) Early changes in muscle: 

After death, early change in body muscle is called the Primary Flaccidity. This is observed in the stage of somatic death and lasts for 1-2 hours after the person has died. During this phase, which occurs soon after death, all the muscles of the body begin to relax. The body flattens over the area that is in contact with the resting surface (contact flattening). The cells in the body are still alive, and anaerobic chemical processes may continue in the tissue cells. (Reddy & Murty, 2014)

Livor Mortis

The final change in the classical triad is livor mortis, which is the purplish-blue discoloration of the skin in the dependent parts of the body due to the collection of blood in skin vessels caused by gravitational pull. Hypostasis develops as spots of discoloration within half an hour to 2 hours. These spots then coalesce into larger patches, which combine to form a uniform discoloration of the body’s dependant parts that have not been subject to pressure, which appears from 6 to 12 hours. The discoloration becomes ‘fixed’ after a certain period, owing to blood cells’ disintegration and hemoglobin’s seepage. This fixation is confirmed by applying pressure with thumbs and is traditionally used to denote a PMI greater than 12 hours.[12] This method of estimation of PMI required an objective and modern approach, leading to the development of colorimetric methods to estimate PMI from livor mortis

The study of death and dying from a variety of reasons  including medical, physical, psychological, spiritual, ethical, and more, is known as Thanatology.

Compiled  & Shared by- This paper is a compilation of groupwork provided by the Team, LITD (Livestock Institute of Training & Development)

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