After death, the human body will typically decompose in a particular predictable fashion, though inevitably subject to a number of variables. To a degree the extent of decomposition can be used to estimate time since death, though an estimation is all this can be, as there is no infallibly scientific means of determining the post-mortem interval. Regardless of other affecting factors, the progression can typically be divided into a number of distinct stages; fresh, bloated, decay, post-decay, and dry/skeletal. Each stage is also associated with a rough time period during which it is likely to occur, subject to the factors that can alter these time periods. Each of these stages are also associated with the arrival of different species of insects, though more can be read about this on the forensic entomology page.
Stages of Decomposition
Fresh (1-2 days)
This stage begins almost instantly from the moment of death. As the heart stops beating, the body’s cells are deprived of oxygen and pH changes occur. Cells gradually lose their structural integrity and begin to break down, releasing cellular enzymes which break down cells and tissues in a process known as autolysis, degraded by the body’s own enzymes. There will be no obvious signs of decomposition, however internally bacteria within the gastrointestinal tract begin to digest the soft tissues of the organs. Throughout this stage certain early post-mortem indicators may begin to occur, such as livor mortis (pooling of blood in the body), rigor mortis (stiffening of muscles) and algor mortis (body temperature reduction).
Bloated (2-6 days)
This stage of decomposition includes the first visible signs of decay, namely the inflation of the abdomen due to a build-up of various gases produced by bacteria inside the cadaver. This bloating is particularly visible around the tongue and eyes as the build-up of gases cause them to protrude. The skin may exhibit a certain colour change, taking on a marbled appearance due to the transformation of haemoglobin in the blood into other pigments. Blood bubbles may form at the nostrils and other orifices. At this point an odour of putrefaction may be noticeable.
Decay (5-11 days)
The previously inflated carcass now deflates and putrid internal gases are released. As the tissues break down the corpse will appear wet and strong odours are very noticeable. Various compounds contribute to the potent odour of a decomposing body, including cadaverine, putrescine, skatole, indole, and a variety of sulphur-containing compounds. Although foul-smelling to most, these putrid compounds will attract a range of insects. Fluids begin to drain from the corpse via any available orifice, particularly the nose and mouth. The internal organs typically decompose in a particular order, starting with the intestines and ending with the prostate or uterus.
Post-Decay (10-24 days)
By the time this stage is reached, decomposition slows, as most of the flesh has been stripped from the skeleton, though some may remain in denser areas such as the abdomen. The previously strong odours of decay begin to subside, though a cheese-like smell may persist caused by butyric acid. If the body has decayed on soil, the area around the cadaver may show signs of plant death.
Dry Stage (24+ days)
The final stage of decomposition results in the remains consisting primarily of bones, some dried skin and cartilage. There is typically no odour of decay at this point.
The core body temperature of a living human being is approximately 37oC, though as would be expected, after death the body will gradually lose heat until body temperature matches the environmental temperature (assuming the temperature of the environment is cooler than that of the body). Although the rate at which body temperature is lost has been investigated, realistically the accuracy of this will be questionable, as body temperature loss is affected by a range of factors including the clothing worn by the victim, the environment, how the body has been left (uncovered, buried, etc), and the victim’s body weight to name a few.
Also referred to as hypostasis or lividity, this typically occurs relatively soon after death, generally becoming apparent within an hour or two. As circulation of the blood stops when death occurs, the blood within the body follows gravity and settles at the lower parts of the body. This results in the visible pooling of blood and a certain discoloration. As livor mortis initially sets in, the discoloration is still temporary and could be disturbed if the body was moved. However after approximately 9 hours or more, the discoloration will be fixed and cannot be changed. Any pressure caused by tight-fitting clothing or ligatures will prevent hypostasis, referred to as pressure pallor.
Perhaps one of the more well-known post-mortem processes, rigor mortis refers to the stiffening of body muscles due to certain chemical changes. After death, the production of adenosine triphosphate (ATP) ceases, a compound which is necessary for normal muscle function. Chemical bridges form between myosin and actin which, without the presence of ATP, are unable to separate, thus ultimately rendering the muscle unable to relax. This state continues until the formed complex is degraded by enzyme activity. This process begins around 2 to 6 hours after death and typically lasts for 24 to 84 hours, depending on environmental temperature and the state of the body. A lower temperature will usually prolong the duration. After this time the muscles then begin to relax. During the time period in which rigor mortis has occurred, the stiffening of the muscles can be broken by physically moving affected areas of the body.
Also referred to as corpse wax or grave wax, adipocere is a grey or light brown waxy material primarily composed of saturated fatty acids, typically formed within approximately one month of death (but has been known to form within up to 6 months). Once formed, this insoluble, waxy material can remain for decades before breaking down. Although development of adipocere may not be entirely understood, the saponification theory states that, in an ideal environment, fatty acids can be hydrolysed from body fat and conjugated with metallic ions such as calcium and magnesium, resulting in the formation of adipocere (Takatori, 2001).
The conditions required for the formation of this substance are relatively specific, occurring best in warm conditions in the absence of oxygen (anoxic conditions) but with high levels of moisture. Various factors can influence the formation of adipocere, including the cause of death, body conditions prior to death, whether the body was buried or not and, if so, how much time passed between death and burial, pH and other environmental conditions. The presence of adipocere can provide certain benefits in establishing time since death as it can help to preserve certain features of the body.
Mummification is a process which typically occurs in warm, arid conditions, ultimately resulting in the desiccation of the body. Similarly, mummified cadavers have also been found preserved in dry, cold conditions. The resulting corpse will often be fairly well preserved compared to cadavers that have undergone the ‘typical’ decomposition process, appearing brown in colour with shrivelled, leather-like skin, retaining certain aspects of the appearance and potentially improving the likelihood of establishing cause of death.
The time taken for a body to decompose can vary greatly due to a wide range of factors that can affect the process. Perhaps the most significant factor in the rate of decomposition is temperature and environment. Warmer temperatures will accelerate the process of decomposition whereas colder temperatures will slow the process down and, if cold enough, stop it altogether. The temperature will equally affect insect succession, which will ultimately affect how quickly the body is broken down. Environmental conditions will equally affect the species of insect present in the area, in turn having an effect on the state of the corpse depending on the species colonizing the remains. A dry and windy environment can dehydrate a cadaver, resulting in mummification (see above).
The amount of protection a body has will also play a role in the rate of decomposition. For instance, a body swaddled in blankets or buried under a few feet of soil will be significantly less exposed than a naked, unburied cadaver exposed to the elements. A protected body may also limit insect activity, resulting in a slower rate of decomposition if insects cannot easily access the corpse, in addition to retaining body heat. If a body is left submerged in water the rate of decomposition will typically be much slower due to the low temperatures and levels of oxygen, unless the corpse is able to float to the surface where insect colonization can occur.
When a dead body is left exposed, it will inevitably attract scavengers which may have an effect on the apparent rate of decomposition. Although insect colonization on remains is reasonably well understood and estimations on time since death can be made by studying these, the cause of death can affect insect succession and in turn the state of decomposition. For instance, a corpse with gaping open wounds may introduce insects into areas of the body sooner than typically expected, resulting in the body appearing to be more decomposed.
If a body was burned the skin and tissue may be charred and dried out, rendering it unsuitable for microbial growth and certain insect colonization. However conversely fire could cause injuries which ultimately expose the body further, accelerating the decomposition process. Though not a common factor that must be taken into account, certain drugs in the body of the deceased have been known to affect decomposition in terms of insect activity. For example, the presence of cocaine has been shown to speed up development of insects, thus having an effect on the state of the corpse.
Human Decomposition Research
The process of human decomposition is still relatively unknown, thus a great deal of research is currently being conducted in hopes of understanding it better. Numerous facilities are now focusing on decomposition research, often referred to as body farms, perhaps the most famous being the Anthropology Research Facility at the University of Tennessee Knoxville. Human remains, often donated, are allowed to decay in a variety of conditions which may simulate real-life scenarios. The result of this research can provide information on the decomposition process, insect succession, and how different factors can affect these procedures. Furthermore, as more research facilities materialise around the world, information can be obtained regarding decomposition in different countries and climates. Current research is also examining the chemicals produced by the body during the decomposition process with the aim of determining time since death based on the volatile compounds emitted at the different stages of decomposition. A better understanding of the intricacies of the decomposition process can ultimately help improve post-mortem interval determination.
Australian Museum. Stages of Decomposition. [online][Accessed 20 Feb 2015] Available: http://australianmuseum.net.au/movie/stages-of-decomposition
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Siegel, J & Mirakovits, K. Forensic Science: The Basics. Florida: CRC Press.
Takatori, T. The mechanism of human adipocere formation. Legal Medicine. 3 (2001), pp193-204.