Human decomposition is a process that begins almost immediately after death and is a typified by many changes. Autolysis of cells results in tissue breakdown and volatile organic compounds that are produced, attract insects.
Two decarboxylation products putrescine and cadeverine are mainly responsible for the foul decomposition odour associated with a body and can be used as scent markers for cadaver dog search and recovery (Statheropoulos et al, 2007; Sorg et al, 2000; Haglund and Sorg, 1997). Decomposition is a complex process and both internal and external factors will influence the rate at which it occurs. Enzymatic breakdown, bacterial action, temperature, rainfall, humidity, clothing, soil, body size, weight, insect activity and carnivore scavenging all play a role (Statheropoulos et al, 2007; Mann et al, 1990).
When documented post-mortem changes and decomposition are arranged in a logical sequence, it is possible to identify the varying stages of decay. These include putrid, bloating, destruction and skeletonisation and occur in a temporal sequence. Since these stages are influenced by environmental conditions and other variables there is no set time frame that can be assigned to them. In standard conditions of 30% humidity and 21 degrees C, many decomposition processes will appear within the first 24 hours post-mortem (Haglund and Sorg, 1997).
Rainfall has little effect on maggot activity already present in the body, however increased rainfall reduces fly activity and thus oviposition (Mann et al, 1990). Trauma to the body has been shown to increase the rate of decay and bodies lying on the surface of the ground decompose more quickly than those that are buried (Mann et al, 1990; Rodriguez, 1985).
In order to contribute to the resolution of legal issues it is important to accurately estimate how long a person has been dead. Estimating the time since death in a forensic case means interpreting the many variables that affect the decay rate of the human body (Mann et al, 1990). Ambient temperature has the largest effect on the decay rate of a body and will be accelerated in warmer weather and decreased in colder temperatures. Flies will visit the body even in low temperatures though eggs will die below zero degrees C. Maggots within the body will continue to feed and develop in freezing conditions as their high metabolic rates produce their own heat. In warm, moist conditions a body can become nearly or entirely skeletonised in 2-4 weeks (Mann et al, 1990).
Decomposition can vary even within the same environment (i.e. from water tables, temperature variation, seasonality, burial depth, etc.) and microbial activity surrounding a carcass increases with shallower burial depth (Wilson et al, 2007). A burial presents a highly complex microenvironment and while decomposition begins almost immediately after death, the speed of post-mortem alteration is influenced by many factors and is highly variable (Wilson et al, 2007; Haglund and Sorg, 1997).