•The irreversible failure of the cardiovascular system (expections occur)
•Following cardiovascular failure, there is failure of oxygen delivery to the tissues resulting in cellular death.
•Energy production ceases and the body cools.
•The circulating blood becomes stagnant and settles under the effects of gravity.
•The usual body defences fail and it can no longer inhibit the proliferation of bacteria - putrefaction ensues
Body temperature after death
•In the first 12 hours, measurement of body temperature is the mainstay (most basic part)
•Rate of body cooling follows a sigmoid shaped curve (in theory)
Factors which influence the rate of body cooling
•Body temperature at the time of death: what is the usual temperature and can it vary?
•Is the body clothed? What is the nature of the clothing?
•Natural insulation of the body!
•The length of the plateau phase of the cooling curve i.e. how long does it take before the body actually begins to cool: the shorter the actual time of death, the greater the significance of the plateau
Why can't stomach content be used to determine time of death
•Too many factors influence the rate at which the stomach empties, e.g. nature/amount of food, solids vs liquids, stress, certain medication
•But, can offer information on what the deceased last ate depending on the condition of the material remaining
•Stiffening and shortening of muscle fibres leading to rigidity of the musculature and fixation of the joints
•Due to the reduction of adenosine triphosphate (ATP) within the muscles after death
•ALL muscle fibres are affected; theoretically detected in smaller muscles before larger muscles
How do you check for rigor?
•Becomes apparent 5-7 hours after death
•Usually full established by 8-12 hours after death
•Dissipates in line with ensuing decomposition and frequently absent by 36 hours after death - body returns to a flaccid state
•Caused by the action of bacterial micro-organisms; process begins at death, but takes a period of time to become detectable
•Variables to be considered: ambient temperature, humidity, “cleanliness” of the environment in which the body lies - may be surprisingly quick or slow!
•2-3 days: greenish discolouration of the abdominal skin
•1 week: blister formation and tissue swelling, including gas formation in body cavities. Vascular “marbling” can be seen due to putrefaction of the superficial veins in the skin
•Certain organs relatively resistant to putrefaction and their persistence can be valuable for identification purposes.
•A process of “dry” decomposition, with desiccation of the body and a relative lack of bacterial involvement
•Body essentially “dries out”; the facial features and hands/feet may become rigid
•Preservation may be remarkable
•Infant bodies particularly prone to mummification
•Induced by the alteration of fatty tissue within the body into a greasy/waxy or brittle material which frequently remains attached to the bony skeleton and may retain the body structure to some extent
Tends to occur in damp or wet environments, e.g. bodies recovered from water
•The condition when all of the soft tissues of the body have completely degraded
•The process is extremely variable: main variables are exposure to meat-eating animals (post mortem animal predation, e.g. rats) and to dipterous larvae
•Radioisotopes have been used to “age” bones, recently including strontium and polonium
Post mortem Hypostasis
•Other terms: PM lividity or PM staining
•Represents the pooling of stagnant blood in dependent regions of the body under the influence of gravity
•Usually readily apparent on the external aspect of the body, but may also be observed in the internal organs
•Begins as soon as the circulation of blood ceases, but takes time to become visible, usually about 1-2 hours, and fully established by 6-12 hours
•Where the body surface has pressure applied there will be compression of the blood vessels, preventing ingress of blood, demonstrated by areas of “pressure pallor” within hypostasis, e.g. a body lying on its back (face up) would be expected to have areas of pallor on the upper back and the buttocks as these are the main areas upon which the body mass rests
Post mortem Artefacts
•Alteration or damage to the body occurring after death which may mimic genuine processes occurring in life
•Resuscitation (cardiopulmonary resuscitation)
•Animal predation (land and sea)
•Traumatic injury, e.g. dead person run over by a motor vehicle or dropped during removal from the scene of death. Bodies recovered from water frequently have some post mortem artefacts due to the movement of the body in the water