Outline
The definition of the ‘moment of death’ had been constantly redefined, given the advent of technology and treatment, which made the prediction of time of death complicated. The need to establish the time of death is very crucial and necessary in criminology. One of the challenging tasks for forensic scientists and detectives is to establish the time of death. The time of death is determined by several methods. Given the influence of several factors on the cadaver, establishing the time of death require to take all these into consideration when estimating the time of death. However the emerging techniques and methods help forensic scientists to constantly and reliably improve their estimate of the time of death.
Introduction
There are several methods to determine the time of death, which however are all associated and dependent on several factors, whose incorporation and level of incorporation has a bearing on the estimated time of death. A commonly recurring problem in forensic science is the fixing of the time of death, within a certain limits. It is perceived that the estimated probable time of death, would have a range, proportional to the time interval between death and examination of the body. The longer the gap between death and post-mortem, the higher would be the reliability on environmental evidence compared to evidence from anatomical changes. The time between the occurrence of death and the discovery of the corpse is called the post mortem interval.
The need to establish the time of assault and death has immense bearing on the criminal justice processes. The time of lethal assault can help in verifying a suspect’s alibi, whether he or she was involved with the crime, based on the time of occurrence. When deaths due to fire are claimed, it is important to determine if the death occurred during the fire or before the fire and also the cause of death. In case of infanticide, the prosecution needs to establish that the child was born alive and later killed. With regard to water, when a body is recovered, it is important to determine if the death was caused in water or the victim killed and then brought into water, based on time of death. There are many methods to establish the time of death, which are all however dependent on several factors.
Defining death.
At one time there had been a controversy as to how death is to be pronounced. These have been made complicated by the developments in medicine and treatment. At first it was perceived that death occurred when breathing stopped. With artificial respiration, that was changed and death due to respiratory failure alone could be averted. This then introduced the concept that stoppage of heartbeat signalled death. However with the advent of cardio pulmonary resuscitation, cessation of heartbeat alone could no longer be considered death. In 1981, the President’s Commission for the Study of Ethical Problems in Medicine and Biomedical Research published a report in which it emphasized death as having occurred when there is an irreversible end of life. This is indicated when circulation and neurological functions are irreversibly stopped.
Practically an individual declared dead can have four or five points of time that are significant to determining death (Lynn and Cranford, 1999). The time 1 is the time when the patient loses the critical function like circulation or become comatose. Time 2 is the time at which the patient or victim is examined and determined to have lost the critical function. The time 3 is the time when the individual’s loss condition becomes irreversible. This is often not apparently known. Time 4 is when this irreversibility loss is determined, subsequent to which death is pronounced at a time 5. Time 4 and time 5 are generally immediate. Resolving the issue of the time of death is very likely to have public discomfort given the practices associated with it.
Methods and sources of evidence
Forensic investigators look at all possible sources associated with the cadaver to estimate the time of death. The time of death may be estimated from the following sources:
• Corporal evidence i.e. Evidences observed in the body
• Environment related evidences i.e. evidence at the vicinity
• Anamnestic evidence i.e. evidence based on the normal habits, movements of the deceased person
All the three sources need to be explored before concluding the nature or time of death (Centre for Forensic & Legal Medicine, 2010). The time of death can be estimated by two methods.
• The rate method: Here the time of death is determined by taking into account the changes produced due to processes. These changes are a result of certain processes that are either initiated or stopped by the occurrence of death. The post-mortem stages are measured along with the transformation of the body. For instance the body changes like cooling rates or algor mortis and changes in stiffening or rigor mortis.
• The concurrence method: Here the occurrence of events at established times are correlated with the occurrence of death. For example, the extent of digestion of the last known meal, the stopping of the wrist watch due to the lethal blow etc.
Subsequent to death, many physico-chemical changes occur in the body in a methodological and sequential manner. These continue until the body is disintegrated. Each change occurs at particular rate of time, which however is also influenced by endogenous and environmental factors. Post-mortem changes are those changes evident in a dead body which can be segregated as ‘early post-mortem changes’ and decomposition. Among the important post-mortem changes are livor mortis, rigor mortis and algor mortis which are the ‘cardinal signs of death’ (Prahlow, 2010). However as several parameters have a role in influencing the rate or nature of the change, the time of death cannot be determined based on post-mortem changes alone.
Algor mortis
Algor mortis or body cooling is considered by many as the single most useful indicator for the time of death, within 24 hours of death. The core temperature of the body is measured based on which the assessment is made. When alive the body is maintained at a constant temperature by the circulatory, nervous and the respiratory system. However upon death, the heat generation is stopped and the body begins to cool down. Forensic investigators determine the temperature of the corpse by inserting a thermometer into the liver. The rate of heat loss by the corpse is determined, based on which the time of death is determined. At about an hour into death, the body cools at a rate of 0.78°C per hour (Bertino and Bertino, 2009). After about twelve hours into death, the body cools at a rate of 0.39°C per hour till the temperature of the body equals that of the surrounding. However this would vary depending on the existing conditions. The rate of heat loss would be higher in cooler or windy environments. The environmental conditions and the temperature of the surrounding air is noted when a body is found. The time of death reached based on body temperature calculations is always expressed in terms of a time range as it cannot be exactly calculated. The rate of post-mortem cooling is based on several cadaveric and environmental factors (Centre for Forensic & Legal Medicine, 2010) including:
1. The size of the body: The bigger the size of the body, the slower would be the heat loss. When the surface area of the body relative to body mass is bigger, the more rapid is the cooling. Thus small bodies like that of children lose heat more quickly than that of adults as they have a greater surface area/mass ratio. Also, the position of the body whether in foetal position or extended position, has a bearing on the heat loss.
2. Clothing: Clothing and coverings insulate the body from its surroundings, thus hampering the cooling process.
3. Immersion in water: When immersed in water, a cadaver cools more rapidly than in air as water is a better conductor than heat. This cooling is more in flowing water.
Livor mortis
Livor mortis or lividity, also described as ‘dependent hypostasis’ is the first condition to set in after death. This condition is associated with the settling of blood, subsequent to the death. Blood constantly circulates in a live body but stops upon death, settling according to gravity. With the settling of blood, the skin that is in contact with the ground become evident. Lividity is not observed in areas where the body is in contact with the ground. Due to the ground pressure in these areas, blood is prevented from reaching them. Areas where lividity is observed, a dark red purple color is seen, within a couple of hours (Prahlow, 2010). This however is difficult to be recognized in dark skin. The areas devoid of blood are described as ‘blanched’. When pressure is removed, the blanched areas gets filled with blood. However after about twelve hours or more, livor mortis become ‘fixed’, where change in blanching with pressure change is not easily observed.
Lividity is first evident after about 20 to 30 minutes into death, evident as dull red spots which deepen in intensity. In the subsequent hours it spreads to extensive areas, becoming more reddish purple. The color and distribution of post-mortem lividity is highly relevant in medico-legal practices, for determining the cause of death. However for establishing the time of death, the development of lividity is too varied (Centre for Forensic & Legal Medicine, 2010).
Rigor mortis
A total muscular relaxation or primary muscular flaccidity is immediately evident after death. This is generally followed by muscular stiffening, a condition called rigor mortis. When rigor is fully developed, the body joints become fixed, with the flexion or extension of joints depending on the body position during death. When a body is moved before the development of rigor, the joints would get fixed corresponding to the new position of the body. Rigor mortis is associated with physico- chemical changes in muscle protein and is relevant to both voluntary and involuntary muscles. Rigor is perceived to develop sequentially and pass off in the order in which it developed.
The onset, rate of progression of rigor mortis has all been correlated with various time intervals. As the rigor development involving temporo-mandibular joint, shoulder joint and other joints are sequential, the sequence of developments in rigor mortis is a valuable tool for determining early post-mortem interval (Shapiro, 1950). The rate, progression and the disappearance of rigor mortis is affected by several variables like higher atmospheric temperature, humid atmosphere and even air movements.
Vitreous humour
The use of vitreous humour for estimating the time of death is also one of the preferred methods as vitreous humour is available in large volume and is generally free from all contamination. There is an orderly increase in the vitreous potassium levels after death, which is used in estimating the time of death. The amount of potassium in vitreous humour is about 2.6 to 4.2 meq/lit., when alive. Potassium enters vitreous humour through the ciliary body as observed by the radioscope technique. A linear rise in the concentration of vitreous potassium was determined with increasing post-mortem intervals. The vitreous potassium levels increased for up to 24 hours after which there is no significant rise (Agrawal, Gupta and Bhasin, 1983). The concentration levels were determined to be almost similar for both the eyes. This increase was also found to be independent of the age and sex of the deceased person. The rate of increase in potassium concentration was about 0.5 meq/lit/hour for up to 24 hours. Measuring the rise in vitreous potassium levels is a simple and comparatively, a more accurate method to estimate the time of death.
With developing technology and methods, there are not only improvements in the existing methods but also the emergence of newer methods for determining the time of death. Forensic entomology and RNA analysis for instance are relatively new techniques that look very promising.
Forensic entomology.
Necrophagous insects play an important role in the decomposition of the cadavers. Forensic entomology focuses on the association of insects with corpses in medico criminal investigations. While several techniques can be used to establish the time since death, these are ideally suitable for two or three days from death. However post-mortem intervals from one day to several weeks can be estimated based on the insect stages and species of the insects feeding on corpses (Amendt, Krettek and Zehner, 2004). Although entomological methods may have difficulties in identifying the insect species, newer DNA techniques help in identifying the Necrophagous insect species.
Forensic entomology was first used in a French courtroom in 1850, to prove a building’s current user was not involved in a murder. A dead body of a child was found near the building and the forensic examiner gave the opinion that, from the development of adult flies, it was evident that the body had been there for about a year. Today forensic entomology has come a long way. Elaborate developments have taken place to identify insect species and their developmental stages. Understanding the chronology of insects that colonize particular areas of corpse and an analysis of the fauna on it, can be used to estimate the time since death. Species identification is also carried out under genetic examination, through DNA isolation and sequence analysis. Studying the effects of toxic substances on insect development is Entomotoxicology. Entomotoxicology is also applied to determine if the deceased person had ingested any drugs or toxicants.
Bloodstains
Bloodstains observed at the crime scene too can provide clues as to whether they have been only recently deposited or have been there for quite a long time. Sometimes blood stains could have been deposited previously due to unrelated events. However emerging and innovative techniques help in establishing the age of the blood stains, which help forensic scientists to determine the time of death with more accuracy (Enotes, 2010). While forensic DNA analysis can identify to whom the blood belonged to, it cannot help in understanding when the stain occurred. Here characteristics of haemoglobin like solubility and color are used to estimate the blood stain age. The use of bloodstain RNA (ribonucleic acid) for determining bloodstain age seems to be very effective. The three types of RNA namely mRNA, tRNA and rRNA decay at various rates.
Conclusion
Establishing the time of death is a big challenge for forensic scientists. Corpses help scientist to reconstruct the circumstance under which the unexplained death took place. (Robert, 2000). Although there are several methods to estimate the time of death, the effectiveness of these methods depends on the factors considered and the extent to which they are considered too. However with improving technology and techniques, investigators are more accurate in their predictions. Newer and elaborate techniques provide more ease and accuracy for the estimations.
