Once death occurs, human decomposition takes place in stages. The process of tissue breakdown may take from several days up to years. At all stages of decomposition, insect activity occurs on the body. The fresh stage of decomposition occurs during the first few days following death. There are no physical signs of decomposition during this time. However, homeostasis of the body has ceased, allowing cellular and soft tissue changes to occur because of the process of autolysis, the destruction of cells and organs due to an aseptic chemical process. At this point, the body enters algor mortis, the cooling of the body's temperature to that of its surroundings. When the body s cells reach the final stage of autolysis, an anaerobic environment is created, that is, an environment wherein oxygen is not present. This allows the body s normal bacteria to break down the remaining carbohydrates, proteins, and lipids. The products from the breakdown create acids, gases, and other products which cause volatile organic compounds (VOCs), and putrefactive effects. VOCs are produced during the early stages of human decomposition.
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Substances produced during the fresh stage of decomposition attract a variety of insects. Diptera insects begin to lay their eggs on the body during this stage, especially member of the Calliphoridae family of insects.
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If the body is on the ground or buried in soil there is also considerable insect activity by the insects that live in the soil around the body. The reasoning for this is simple: A dead human body serves as an excellent source of decaying matter to feed on and in such a hospitable environment.
Odor, color changes, and bloating of the body during decomposition are the results of putrefaction. The lower part of the abdomen turns green due to bacteria activity in the cecum. Bacteria break down hemoglobin into sulfhemoglobin which causes the green color change. A formation of gases enters the abdomen which forces liquids and feces out of the body. The gases also enter the neck and face, causing swelling of the mouth, lips, and tongue. Due to this swelling and misconfiguration of the face, identification of the body can be difficult. Bacteria also enter the venous system causing blood to hemolyze. This leads to the formation of red streaks along the veins. This color soon changes to green, through a process known as marbelization. It can be seen on the shoulders, chest and shoulder area, and thighs. The skin can develop blisters containing serous fluid. The skin also becomes fragile, leading to skin slippage, making it difficult to move a body. Body hair comes off easily. The color change of the discoloration from green to brown marks the transition of the early stage of putrefaction to the advanced decompositional stages.
After the body goes through the bloating stage it begins the black putrefaction stage. At this point the body cavity ruptures, the abdominal gases escape and the body darkens from its greenish color. These activities allow for a greater invasion of scavengers, and insect activity increases greatly. This stage ends as the bones become apparent, which can take anywhere from 10 to 20 days after death depending on region and temperature. This period is also dependent on the degree to which the body is exposed.
After the early putrefaction and black putrefaction phases have taken place, the body begins mummification, in which the body begins to dry out. The human carcass is first mummified, and then goes through adipocere formation. Adipocere (grave wax) formation refers to the loss of body odor and the formation of a cheesy appearance on the cadaver. Mummification is considered a post-active stage because there is less definite distantion between changes and they are indicated by reduced skin, cartilage, and bone. Mummification is also indicated when all of the internal organs are lost due to insect activity.
When the last of the soft-tissue has been removed from the body, the final stage of decomposition, skeletonization, occurs. This stage encompasses the deterioration of skeletal remains, and is the longest of the decomposition processes. Skeletonization differs markedly from the previous stages, not only in length, but in the deterioration process itself.