POSTMORTEM CHANGES AND

DETERMINATION OF THE TIME OF DEATH

I.  Introduction 

After death, a number of changes take place in the human body. For several reasons, it is vitally important that anyone involved in death investigation be familiar with these postmortem changes. First of all, some of the changes which take place progress at a known, steady rate. By observing the extent to which a particular change has progressed, and by knowing the rate at which that change progresses, an estimation of the time since death can be made. Second, some of the changes which occur after death can be mistaken by the uninitiated for injuries sustained before death. Finally, the decomposition process may alter or obliterate true antemortem injuries, making determination of the cause of death difficult. 

The following sections will discuss each of the major postmortem changes, along with their usefulness in determining the time of death. A final section will address the overall approach to determining the time of death.

 II.  Postmortem Cooling

A. General Considerations

 During life, body temperature is maintained by the body's metabolism. At death, metabolism ceases, and body temperature begins to approach the ambient (environmental) temperature which is almost always lower than body temperature. For many years, researchers have noted a roughly linear relationship between body temperature and the time elapsed since death. However, many factors affect this relationship, and this method of determining time of death should not be the sole method employed.

 B.  Formulae utilizing body temperature to determine time of death.

 A number of formulae have been employed to relate the body temperature to the time elapsed since death.

 Body cooling is by radiation, conduction and convection. Body warmth is lost from the surface to the surroundings. Because of this, the core temperature remains relatively static for the first 1-2 hours after death. Thereafter, body temperature drops approximately 1.5 degrees per hour. In any case, body temperature will usually approximate that of the environment within 20-30 hours.

 C. Variables affecting postmortem temperature decline.

 1. Assumption of normal body temperature.

 Normal body core temperature is 99.6 F, and certainly many individuals die with that particular body temperature. However, there are factors which may raise or lower a person's body temperature at death. Conditions which increase body temperature include intense physical activity, drugs (e.g. cocaine), and fever due to natural illness. It is also possible for a person to have a significantly low body temperature prior to death (hypothermia).

 2.  Assumption of "standard" rate of temperature decline.

There are a number of factors which affect how quickly body temperature will drop after death. Body cooling is fairly complex, and relies on a variety of mechanisms.

 a.  Humidity. The rate of cooling depends, to a certain extent, on evaporation. The rate of evaporation is in turn dependent on humidity. In other words, a body in a humid environment would cool relatively slower than the same body would in a drier environment.

 b.   Insulation. This may mean clothing, body wrappings, or even body fat. Anything which insulates the body will cause it to cool relatively more slowly.

 c.   Surface in contact with body. Part of the cooling process may involve direct conduction from the body to a contacting surface. If this contacting surface is relatively warm or cool, the rate of cooling may be retarded or accelerated, respectively.

 d.  Ventilation. A well-ventilated environment will speed the rate of cooling, as this would increase evaporation as well as increase heat loss through convection.

 e.   Environmental temperature. The colder the environment, the more rapid the cooling.

III. Rigor Mortis

 A.   General Considerations 

Rigor mortis is a gradual stiffening of the body's musculature which occurs after death. It does not involve any significant shortening of the muscle fibers. It is not a permanent change; under usual conditions, rigor mortis disappears by 48 hours after death. It is believed to result from biochemical changes in the muscle cells. During life and shortly after death, the cytoplasm of the muscle cell is in a liquid state. With increasing time after death, the cytoplasm is converted to a gel (solid) state -- hence the rigidity associated with rigor mortis. With increasing time, the cytoplasm converts again to a liquid state and rigor is gone. There are several important ways in which rigor mortis may aid death investigation. First, rigor usually develops in a typical fashion and over a known period of time. The distribution and degree of rigor can thus help determine the time of death. Second, if rigor is developed in a body, but the position of the body is not consistent with the scene, then one may conclude that the body was moved after death.

 B.   Chronology of Rigor Mortis

 In an average person at ordinary room temperature, rigor usually becomes apparent at 2-4 hours after death. It usually is complete at 12-18 hours after death. It usually begins to go away 24-36 hours after death. And it has usually disappeared 48 hours after death.

 C.   Distribution of Rigor Mortis

 Classically, rigor first becomes apparent in the muscles of the face and jaw and spreads "downward" through the body to involve the trunk and extremities. If an individual was engaged in strenuous activity prior to death, rigor will develop sooner in the muscles used for that activity. Disappearance of rigor generally follows the same pattern, disappearing first in the head and then extending to the trunk and extremities.

 D.   Degree of Rigor Mortis

 Intensity of rigor depends on the decedent's muscular development. The very young, very old, and debilitated have poorly developed rigor. After full development, broken rigor cannot be reestablished. Partly established rigor can be broken, and then partly return.

 1. Grading of Rigor - Very subjective

0 - absent

mild - perceived stiffness in a joint

moderate - difficulty breaking rigor in a joint

full - great force needed to break rigor

 E.  Variables affecting onset and duration of rigor 

As with body cooling, a number of variables affect the rate at which rigor develops. The same caution needs to be exercised with using rigor in determining the time of death.

 1.  Variables which accelerate the onset of rigor

a.     exogenous heat

b.     violent exertion prior to death

c.     seizure activity

d.     alkaloid poisoning

 2.  Factors which delay the onset of rigor

a.          exogenous cold

b.          exsanguination hemorrhage

c.          asphyxial deaths

d.          poisoning by arsenic

F.  Conditions simulating rigor

1.  Cadaveric Spasm

 This is a rare form of muscular stiffening which occurs at the time of death. It usually affects groups of muscles in the arms. It records the last act of life (eg. tight clutching of a knife).

 2.  Heat stiffening

 This process is seen in fire deaths and involves actual cooking of the muscle fibers. Because the fibers shorten, one sees a typical "pugilistic" appearance.

 3.  Cold stiffening

 Fat and muscle become solid at temperatures less than 40 F. Rigor will develop if a body which was frozen before rigor developed is subsequently thawed.

 IV.  Postmortem Lividity (Livor Mortis)

A.  General Considerations

 After death, blood present in the vascular system will settle in dependent portions of the body. The blood settles into the capillaries where it imparts a visible purple-blue to the skin. As with rigor mortis, the development of lividity follows a typical time course which makes it helpful in determining the time of death. After a period of time, lividity becomes "fixed", that is, once developed in an area it will stay there. This feature of lividity makes it helpful if a body has been moved after death.

B.  Chronology of Lividity

 Lividity generally becomes visible between 1/2 and 4 hours following death. It becomes well developed within the next3 to 4 hours , and is maximally developed at 8 to 12 hours following death. Lividity becomes fixed at around 8 to 12 hours following death. 

C.  Other Factors Affecting Lividity

 As mentioned above, lividity is usually purple-blue. In certain other instances, the color of lividity may be different. Cyanide poisoning and carbon monoxide intoxication are associated with red-pink coloration. Lividity may in rare instances have a brown color due to methemoglobinemia (usually associated with over use of certain drugs). In extremely anemic individuals, individuals who have lost a large amount of blood, or in extremely dark-skinned individuals, lividity may not be visible. 

V.  Postmortem Decomposition

 A.  General Conditions

At death, a number of changes begin to take place in the body on the microscopic and biochemical levels. Enzymes are released which begin to break down the body's tissue. Bacteria from the intestine and from around the body orifices proliferate, and also begin to break down the tissues. In time, these processes become grossly visible as decomposition. Decomposition continues until all of the body's soft tissues are gone. 

B.   Chronology of Postmortem Decomposition

 Under "usual" conditions at around 24-36 hours after death, blue-green discoloration of the lower abdomen is visible. This is followed by marbling, which derives its unique pattern from the blood vessels of the skin. Blood in the vessels breaks down and seeps out into the surrounding tissues, resulting in the complex, branching pattern. At 36 to 48 hours after death, bloating of the face and trunk may be evident. The whole body will show decomposition change at 60-72 hours after death. 

C.   Variables Affecting Development of Postmortem Decomposition

The rate at which decomposition develops depends on a number of factors. Whether the body is in the open, in water, or buried will greatly affect the rate of decomposition. Bodies in air will decompose most quickly, and buried bodies most slowly (rule of thumb: 1 week in air = 2 weeks in water = 8 weeks in ground). In general, "increased temperature will increase the rate of decomposition. Insulation in the form of clothing or body fat will retard body cooling and hence increase the rate of decomposition. In general, cold will delay the development of decomposition.

 VI.  Other Postmortem Changes 

A.  Mummification

 This occurs when the ventilation is good, and the environment is dry and warm. Early mummification can be seen after about 1 week on exposed fingers, hands, and toes. If left undisturbed, the process will be complete in 3-6 months. 

B.  Adipocere

 This results from a chemical change in the body's fat. This particular change occurs only in wet or damp environments and takes months to development. The fat is converted to a relatively hard, waxy substance which retains the normal contours of the body.

 C.  Animal Activity

 It is sometimes difficult to differentiate true injuries from changes made by postmortem scavengers. Depending on the environment, such changes can be made by insects, fish, crustaceans, rats, dogs, and many other species. 

VII. Determination of the Time of Death

 A.  General Considerations

The only certain way to determine the time of death is to be there when it happens. From the preceding description of postmortem changes, it should be apparent that evidence from the body alone is insufficient to reach a reasonable conclusion regarding the time of death. Determination of the time of death is a team effort, since a thorough scene examination will not only document vital information about the environment in which a body was found, but also will reveal information unrelated to the condition of the body which will aid in determining the time of death. 

B.  Range of Death

 Careful consideration of all factors will not allow a pinpoint determination of the time of death. At best, a range for time of death can be established. The range of death is the period of time in which death is believed to have occurred. The more available information about a death, the more the range can be narrowed. The widest range "is the time between when the person was last known alive and when the body was found. 

C.  Types of evidence used to determine the time of death:

 1.  Corporal Evidence - evidence from the body, i.e. post­mortem changes.

 2.  Environmental and Associated Evidence

 This includes items such as temperature, humidity and clothing. It also includes information such as whether the newspaper was picked up, if the lights were on, if an alarm clock was on, if a telephone recorder was on, if food was on the stove, or if there were any receipts in the house.

 3.  Personal Evidence

 This includes information regarding an individual's daily habits—when they awake, what they eat, when they come home from work, etc. 

D.   "Calculating" The Time of Death

 After all available information has been gathered, the range of death may frequently be narrowed by environmental and personal evidence. Corporal evidence may then be taken into account to narrow the range as much as possible.