Tag Archives: decomp


AA5Many crime writers mistakenly believe there’s a precise science to pronouncing time of death (TOD). There is a progressive process, but the sequence and time intervals are influenced by many factors. To craft convincing death scenes, authors need to know how a body actually breaks down.

Mortis is the anatomical term for changes in a body after the moment of death. Medically, that’s when the central nervous system gets unplugged and oxygenated blood is no longer delivered to the tissues, which naturally start recycling. The five types of mortis are:

  • Rigor – stiffening of muscles

  • Livor – settling of blood

  • Algor – change in temperature

  • Palor – change in color

  • Decomp – breakdown in tissue

AA6All these mortis conditions are integral to a decomposing process. Death is a part of life and decomposition is a part of death. Just as life is not always predictable, neither is estimating the post-mortem interval (PMI) between when death anatomically occurred and when first examination of the body begins.

Death investigations work on a triangle of Body – Scene – History. It’s a holistic approach to determining cause of death (COD) and it’s the coroner’s responsibility to answer five universal questions:

  • Who is the deceased?

  • Where did they die?

  • When did they die?

  • What caused their death?

  • What was the means of death?

AA7Some people are confused about the difference between cause and means. Cause is the medical reason. In this fellow’s case the cause of death would be traumatic brain injury. Means is the mechanism or physical reason – gunshot wound to the forehead.

There can be thousands of causes of death, but there are only five classifications:

  • Natural

  • Accidental

  • Suicide

  • Homicide

  • Undetermined

AA8How this ties into mortis is that satisfying the five universal questions, great weight is placed on interpreting the body’s condition when first examined. This is where understanding the mortis process is so important and a lot of the interpretation comes from years of experience.

The proper pronunciation of the mortis states puts emphasis on the first syllable and it’s a long ‘I’ (RYE-gore).

Let’s look at each one.

Rigor Mortis is the stiffening of muscles. It’s caused by the body’s energy source, adenosine triphosphate (ATP), being depleted. With no energy left to keep the muscles flexible, they naturally go to a rigid state until another enzyme begins the breakdown of tissue and relaxation returns.

AA10Immediately upon death, the body enters a brief period of primary flaccidity where it’s dead limp. Depending on many factors, temperature and body mass being the big ones, the muscle stiffening begins in 1- 2 hours, first setting into the eyelids, jaw, and neck. It proceeds to the limb joints and extremities after 4-8 hours and fixes in the organs in about 12 hours. Rigor releases in a reverse sequence and can be absent in as little as 12 hours or can stay for days, again depending on factors.

Livor Mortis is the pooling of blood caused by gravitational settling once the heart stopped pressurizing the vascular system. It’s evident by purplish-red blotching where blood is free to pool and blanched-white where pressure points restrict it. Lividity, as it’s also known, sets in between 30 minutes to 1 hour after death and ‘fixes’ in about 8-12 hours. ‘Fixing’ is the entire settling where blood has coagulated and no longer runs free.

Algor Mortis is the change in body temperature. A cadaver will always achieve ambient temperature, regardless of time. A normal, living human’s core temperature is 36 Celsius (98.6 Fahrenheit) but the scene temperature could be anywhere above or below. In a cold environment, the body will drop to equilibriate. In a hot environment, it will rise. Here’s where so many peripheral factors come into play. Body size. Layered Clothing. Air movement. And the list goes on. A rule of thumb is that a body’s temperaature will change about 1 degree Celsius per hour.

AA11Palor Mortis is the change of color. Live humans are pretty much a reddish tinge due to oxygenated blood flowing (different tones for different races). Immediately upon death, a bluing phase occurs, following by a grey, then a white, and it can be a rainbow of colors as decomposition takes over.

Decomp, or decomposition, is not really a true class of mortis – rather it’s the culmination of the four mortis processes which leads to a breakdown of the body tissues and a return to nature.

Decomposition is a complex and unpredictable thing. There are two processes that morph into one:

  • Putrefaction – action of bacteria on body tissues

  • Autolysis – body breakdown by endogenous substances

AA9In most deaths these two work in tandem, starting with a breakdown in internal organs which produces gas. This causes bloating and skin discoloring, as well as the foul odor from purging or ‘gassing-off’. As the muscle tissues change, the skin begins to dislodge, the joints become loose enough to disarticulate, fats become liquefied, and bones become exposed. Advanced decomp can become skeletonized, mummified, or consumed – again depending on so many factors, which all start from the mortis process.

The changes in a human’s body after death can be just as varied as their experiences in life.

Biological, environmental, and circumstantial factors will shape your death, just like they’re shaping your life.

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I originally wrote this post for Kristen Elise, PhD, on her blog site at MurderLab.com. I think it’s useful information for other crimewriters so I shared it here at DyingWords. Here’s the link to the original post on Kristen’s site:



This great guest post is by Andy Brunning, a UK Chemistry Teacher who hosts the fascinating website Compound Interest at www.compoundchem.com .

Decomp1Decomposition is an incredibly complicated process, but we do know a little about the chemical culprits behind some of the terrible smells as the body breaks down.

Before we look at specific compounds, it’s worth taking a look at the decomposition process as a whole.

Decomposition, or ‘Decomp’ as it’s called in the death business, can be roughly divided into four stages: the fresh stage, the bloated stage, the active decay stage, and the advanced decay stage. Some overviews of the process also add in a final stage when all that is left of the corpse is dried remains. This can be skeletal, mummification, or fossilization.

The fresh stage of decay kicks off about four minutes after death.

Decomp2Once the heart has stopped beating, the cells in the body are deprived of oxygen. As carbon dioxide and waste products build up, the cells start to break down as a result of enzymatic processes – these are known as autolysis. Initial visual signs of decomposition are minimal, although as autolysis progresses blisters and sloughing of skin may occur.

The second stage of decay occurs as a result of the action of micro-organisms.

The actions of bacteria on the soft tissue of the body produces a variety of gases which cause the carcass to become bloated and swell in size. It’s claimed that the body can as much as double in size during this stage of decomposition. The sulfur-containing compounds that the bacteria release also cause discolouration of the skin, giving it a yellow-green hue.

Decomp3As a result of the bloating, the increased pressure causes bodily fluids to be forced out of natural orifices, as well as potentially causing ruptures in the skin. This can cause a formidable odour; at this stage, if insects are able to access the body, flies will lay eggs in exposed orifices, which will in turn hatch into maggots which then devour the flesh.

The third stage is that of active decay.

At this stage, the ongoing action of bacteria activity and decomposition leads to the liquefaction of tissues, and the persistence of the strong odour. It is during this stage that the cadaver loses the greatest mass.

The final stage, advanced decay, occurs once most of the cadaveric material has already decomposed.

A wide range of factors can affect the decomposition process, including whether the body is buried, and the ambient temperature.

Decomp4These factors also have an effect on the large number of compounds produced during the decomp process. Considering that, as a species, we’ve been dying and decomposing for thousands of years, we know surprisingly little about the specifics of the process and the chemicals involved.

What we do know is that there are several key compounds that contribute towards the characteristic odours of decay.

Two of these are pretty much named for this contribution: cadaverine and putrescine. The aroma of both is loosely described as ‘rotting flesh’, and they have relatively low odour thresholds – meaning that not a lot is required in order for them to make their presence felt by your nostrils. Oddly enough, their presence in your body isn’t limited until after you die, however. Both crop up in cases of oral halitosis (i.e. bad breath), as well as in urine and semen, contributing to their odours.

Two other key compounds are skatole and indole.

Decomp6Skatole, as you may have already guessed from the name, has a strong odour of faeces, whilst indole has a mustier, mothball-like smell. Both compounds are found in human and animal faeces, so it’s little surprise that they can contribute unpleasantness to the odour of a decomposing corpse. The strange thing about both is that, at low concentrations, they actually have quite pleasant, flowery aromas, leading to an array of unexpected uses. Indole is found in jasmine oil, which is used in many perfumes, whilst synthetic skatole is used in small amounts as a flavouring in ice creams, as well as also being found in perfumes.

A range of sulfur-containing compounds also contribute to the smell of decomposition.

Decomp7Produced by the action of bacteria, compounds such as hydrogen sulfide (which smells of rotten eggs), methanethiol (rotting cabbage), dimethyl disulfide (garlic-like) and dimethyl trisulfide (foul/garlic) all add to the unpleasant scent. A whole range of other compounds are also produced as the tissues of the body decompose – some studies have identified over 400 different compounds, although not all of these will be contributors to the odour.

There’s still a lot we don’t know about decomposition.

Decomp8Using human corpses in research on decomp is limited in many countries for ethical reasons, so in many studies pigs are used as models. In the USA, however, there are a number of ‘body farms’ – facilities set up in a several states to study decomposition of human remains. The bodies they study are those who have chosen to donate their remains; these are then allowed to decay in a range of conditions and studied as they do so. This can help researchers determine the appearance and chemical emissions of bodies at various stages of decay, which can then inform police investigations where bodies are discovered, helping to determine a more accurate time of death.

Our knowledge about decomposition will develop over the coming years as more studies are carried out.

A particular area of development is looking at producing a method of determining time of death from volatile compound emissions, as the different groups of organic compounds are emitted in varying levels at different stages of the decay process.

Chemistry-of-Decomposition (1)

Compound Interest is a blog by Andy Brunning, a chemistry teacher in the UK, creating graphics looking at the chemistry and chemical reactions we come across on a day-to-day basis.

Decomp10Check out Andy’s fascinating site at www.compoundchem.com