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Pallor mortis - the paleness that is associated with death; it results from the fact that the blood is no longer at the skin’s surface because circulation has ceased.

Full paleness happens in the first 3 hours after death.

It is difficult to quantify the progression of this process, however, so this change generally is of little value in determining the time of death.

Algor mortis - the cooling of the body’s temperature following death as it falls from the static 98.6 degrees Fahrenheit to the ambient temperature.

A body’s temperature, usually measured using a rectal thermometer, provides some information that is useful in estimating the time of death.

However, bodies do not all cool at a consistent rate, so a somewhat complex equation must be used.

Many factors can influence the rate of a body’s cooling, including the presence of excessive humidity, lack of humidity, and the body’s position near a heat source (such as a radiator), so any estimation has a wide margin of error.

Rigor mortis - the stiffening of the body’s muscles after death.

The muscles become so stiff that they are nearly impossible to move or manipulate.

If the entire body is moved from its position at death while rigor mortis is fully established, the body’s limbs will maintain their original pose, appearing to defy gravity.

The cause of rigor mortis is a chemical reaction in which water reacts with the body’s adenosine triphosphate (ATP), the chemical energy source required for movement in living tissue and converts it to another compound.

Rigor mortis follows what is typically referred to as the “rule of twelves.”

It normally takes the first 12 hours after death for rigor mortis to set fully, starting with the small muscles such as jaw and eyelids, then moving to the facial muscles, all the voluntary and involuntary muscles.

The body becomes completely rigid after the first 12 hours.

The body stays in full rigor for the next 12 hours (12 to 24 hours after death), and then rigor begins to release during the third 12 hours (24 to 36 hours after death).

After 36 hours, the rigor mortis is fully released, and the body is once again limp.

Knowing what stage of rigor mortis a body is in can help in the determination of time of death, but many factors—such as ambient temperature, antemortem physical condition, and humidity—can vary the rigor schedule by hours.

A body’s stage of rigor mortis can be very helpful in the determination of whether the body has been moved.

If a body’s limbs appear to be defying gravity or

the body is in a position that does not make sense given the circumstances (leaning against a wall instead of crumpled on the floor, for example), investigators can conclude with certainty that the body was moved several hours after death.

Livor mortis - occurs when the blood, no longer in circulation, passes through the capillaries to settle in the gravity-dependent areas of the body.

The blood stains the skin a dark red color in those areas.

Lividity, as this process is also called, begins within the first hour of death and continues until full staining occurs at approximately 12 hours after death.

An estimation of time of death can be made based on how deeply the skin is stained, but such an estimation is not specific and cannot be made until after full lividity is reached.

If the body is moved before full lividity is reached, the blood will shift and settle in the new gravity-dependent areas of the body.

Partial staining may have already occurred in the original position, meaning the body has dual lividity.

The only way dual lividity can occur is if the body is moved after death and prior to full livor mortis.

Another sure indication that a body was moved after death is if it has reached full livor mortis, but the staining is not in the gravity-dependent areas of the body.

In other words, if a body has full lividity of the chest but is found lying on its back, then full lividity was reached while the body was facedown, after which the body must have been flipped over.

Autolysis and Putrefaction

Autolysis - the destruction of a cell after its death by the action of its own enzymes, which break down its structural molecules.

Human cells have an organelle known as the lysosome, which is a membrane containing up to forty digestive enzymes that are made by the endoplasmic reticulum and Golgi apparatus (sometimes called the Golgi complex).

The lysosomes are responsible for digesting nucleic acids, polysaccharides, fats, and proteins within the cell.

They are active in recycling the cell’s organic material and in the intracellular digestion of macromolecules.

At the point of death, these enzymes are released from the lysosomes’ membranes and begin destroying the cell.

Putrefaction - the breaking down of flesh and tissue caused by bacteria, creating the strong odor associated with decomposition.

Putrefaction usually begins concurrent with autolysis in the first stages of decomposition.

The stages of putrefaction vary, as do the times within each stage, depending on environmental conditions.

Some of the factors that influence the speed of putrefaction include: the atmospheric temperature and humidity level, the movement of air, the state of hydration of the tissues and the nutritional state of the body before death, the age of the deceased, and the cause of death.

Low temperatures, which inhibit the growth of bacteria, retard the process considerably.

One of the earliest signs of putrefaction in human decomposition is the discoloration of the lower abdominal wall near the right hip bone because of the proximity of the cecum and large intestine to the skin’s surface there.

Human bodies house many bacteria that assist in the digestion process.

After death, as intestinal bacteria begin the putrefaction process, the lower-right abdomen turns a greenish to black color.

The gases produced by the bacteria are also responsible for swelling of the face and neck.

This swelling may cause the eyes and tongue to protrude and may make visual identification of the decedent difficult.

Other effects produced by the gases include a marked increase in the volume of the abdomen, which is under tension, and of the scrotum and penis, which may become larger than normal.

The intestinal bacteria begin colonizing the entire body, using the venous system as pathways.

The discoloration of the abdomen eventually spreads as the bacteria migrate, changing the veins and arteries of the rest of the abdomen, the thighs, the chest, and the shoulders to the same green and black.

The discolored venous system makes visible lines across the body; this is referred to as marbling.

A few days to a week after death, as the bacteria continue to devour tissue, the skin begins to blister in the sloping regions of the body.

Eventually the blisters, which contain a thick reddish liquid, erupt, making the epidermis (the outer layer of skin) fragile.

Ultimately, the epidermis becomes so delicate that it tears easily and may come off in large areas, leaving the red dermis below visible. This phenomenon is referred to as skin slippage.

At times, the epidermis of an entire hand may detach, creating a glove of skin.

If the skin of the fingertips detaches, identification of the body through fingerprints may be difficult, but as long as the fingertip skin is still available, fingerprints may be retrievable.

Forensic scientists have had success in placing such skin over their own latex-gloved fingers to retrieve the fingerprints.

As the body enters the second week following death, the increased pressure on the abdomen produced by putrefactive gases leads to the ejection of feces and urine.

This pressure also leads to the expulsion of liquids from other body orifices, particularly from the mouth and nostrils.

Because this liquid is often bloody, its presence sometimes leads to a misdiagnosis of injury.

At this stage, the orifices as well as the organs may take on a foamy appearance as the gases mix with liquids internally.

In the following weeks, the skin begins to darken to black, making identification even more difficult.

The face becomes even more bloated and blackens as well, so that racial characteristics may be masked.

The cadaver continues to bloat with internal gases, giving the impression that the deceased was a very heavy individual.

Internal decomposition of the organs tends to occur at a slower pace than that of the rest of the body.

The capsules of the kidney, spleen, and liver resist putrefaction more than do other tissues, but eventually they become sacs containing a thick reddish liquid.

These sacs will ultimately burst.

The viscera and soft tissues disintegrate, whereas organs such as the uterus, heart, and prostate last longer, as do tendon tissues and ligaments attached to the bones.

These different rates of decay of the organs may be proportional to the amounts of muscular and conjunctive tissue they contain.

Saponification

Decomposition tends to be slower in water than in air because of the usually lower temperature of water, which retards bacterial growth.

Water also protects the body from insects and predatory animals, with the notable exceptions of certain birds and fish.

A body typically floats head down because the head does not develop gas formation as easily as the abdomen; this causes fluids to gravitate to the head.

Putrefaction of a body that has been decomposing in water is thus more visible on the face and front of the neck, making visual identification particularly difficult.

Identification is further hampered by saponification, which is a chemical process in which water converts the body’s fatty acids into a different compound called adipocere.

A grayish-white or tan spongy substance that adheres to the body, adipocere can act as a preservative, counteracting the effects of decomposition.

Saponification requires at least partial immersion of the body in an aquatic environment with warm temperatures.

It normally presents as peeling, blanched skin.

Adipocere has been found on bodies in bathtubs, ponds, lakes, and oceans.

It has also been discovered on bodies inside caskets, on bodies found in caves, and on remains wrapped in plastic.

Mummification

Mummification - the process of drying out the tissues of a body. It is characterized by

dryness and

brittle, torn skin, especially on the protruding areas of the body, which is generally brown in color.

It is possible for slight adipocere to form in mummified bodies, as the hydration needed to create the fats contributes to the drying of the body.

Mummification is found in dry, ventilated environments and generally in warm places where bodies lose fluids through evaporation.

Mummification is often found in desert environments, but it can also occur in dry, closed spaces, such as attics and closets.

Dehydration before death may contribute to the process of mummification.

Mummified bodies are often found in a state of preservation, so that it is usually much easier to investigate the identities of the deceased than it is in cases of saponification.

Performing an autopsy on mummified remains is very difficult because the skin is extremely brittle and disintegrates easily.

A variety of methods have been developed to rehydrate mummified bodies for better autopsy results.

This rehydration is often referred to as tissue building.

Skeletonization

Skeletonization - (or the removal of all soft tissue from the bone) is generally considered the last stage of decomposition. It may be:

complete, meaning the entire body has no flesh, or

partial, with areas of the body in different stages of decomposition.

Under normal conditions, skeletonization occurs only after a considerable amount of time has passed.

An unembalmed adult body buried 6 feet deep in ordinary soil without a coffin normally takes 10 to 12 years to decompose fully to a skeleton, given a temperate climate.

If a body is immersed in water, skeletonization will occur approximately 4 times faster; if it is exposed to air, the process will be 8 times faster.

The intervention of predatory insects or animals can greatly speed up this timetable.

Insect and Predator Activity

Predatory insects and animals can accelerate decomposition by:

eating the flesh of a cadaver,

separating the body into parts, or

using the body as a repository for their eggs.

The involvement of insect predators in particular can be beneficial to investigators in that it can help in the determination of an estimate of time of death.

Insects are the first organisms to arrive on a body after death.

They colonize the remains in a predictable sequence, as each stage of decomposition, from fresh body to skeletonization, is attractive to a different group of insects.

When remains are found weeks or months after death, the examination of insect evidence is often the only method available that can help investigators to determine an approximate time of death. 

Forensic entomologists study what insects are present in and on the body and pinpoint the development stages of those insects.

They also take note of the species that are not present.

Every group of insects that has inhabited the body will have left evidence of having been there, even the groups that have moved on as the body progressed through successive decomposition stages.

Blowflies, which can detect death from great distances, are the first to colonize a body.

Overall, studying decomposition is vital for forensic pathologists and investigators in unraveling the circumstances surrounding a person’s death.