Rigor Mortis: What is it and how is "time of death" established?

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Rigor Mortis, what is it and how does it help pathologists to determine a person’s “time of death”? Before, we understand rigor mortis, we need to determine what is death?

There are three stages before death can be determined; respiratory, cardiac and neural; once a human body goes into respiratory arrest, the lungs stop and oxygen is no longer produced; once a human body goes into cardiac arrest, the heart stops, and that oxygen rich blood can no longer be pumped to the vital organs which keep us alive, including the brain. Brain cells can die if they are deprived of oxygen for more than three minutes, and once the brain is dead, the person is dead.

Rigor Mortis is just one of several stages which pathologists use to determine a time of death, including decomposition, which we’ll focus on next week, but these are the first four:

#1 Pallor Mortis (which in Latin literally means “paleness of death”), it’s where the skin rapidly becomes whiter or paler, owing to a lack of blood circulating through the body’s capillaries, it begins within first 15-25 minutes of death and can last up to two hours, but how pale a person becomes does not denote how long they’ve been dead, as all skin-tones are different.

#2 Algor Mortis (which in Latin means “coldness of death”), where owing to a lack of fresh warm blood circulating, the body begins to cool in a slow and steady decline. Excluding external factors such as clothing, disease, drugs, alcohol and the environment, the human body has an average rectal temperature of 36.9 Celsius / 98.4F, but after death, this reduces by an average of 2 degrees Celsius in the first hour and 1 degree for every hour after that, until the body matches or nears the ambient temperature of its environment. The only time the body temperature naturally changes is during decomposition, when (owing to chemical changes in the body) the temperature increases.

#3 Rigor Mortis; (which in Latin means “stiffness of death”), this is the rigidity of different parts of the body caused by a chemical change in the muscles, rigor mortis can occur after 2-4 hours, it reaches maximum rigidity after 12 hours and slowly dissipates over the next 72 hours, until rigidity has ceased. The face and the neck are affected first, then the limbs, with the eye and mouth muscles often opening and becoming fixed after death, which gives corpses a shocked or haunted expression.

And #4 Livor Mortis (Latin means “blueish colour of death”), this is when (as the heart is no longer circulating the blood) gravity causes the heavier red blood cells to sink to the lowest part of the body, this begins in the first 20-30 minutes after death but isn’t visible until two hours later, with the size and the discoloration of the patches reaching its maximum 8-12 hours after death.

So, although Rigor Mortis is vital for pathologists, it’s really a combination of these four factors (Pallor Mortis - paleness, Algor Mortis - coldness, Rigor Mortis – stiffness and Livor Moris – colour) which can help determine a time of death, as well as at what state of digestion the victim’s last meal is in their stomach, whether the optic fluid in the eye had begun to dry, the elasticity of the skin, which different microbes remain in the victim’s mouth, the coagulation of the blood (for very recent deaths), and the different flies or larvae which have begun to feed or gestate in the body.

Yummy. And if you were listening to that, whilst part way through a lovely meal? If you haven’t put your knife and fork down yet, I wouldn’t tuck back in for at least another ten minutes, if I were you.

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Michael J Buchanan-Dunne is a writer, crime historian, podcaster and tour-guide who runs Murder Mile Walks, a guided tour of Soho’s most notorious murder cases, hailed as “one of the top ten curious, quirky, unusual and different things to do in London”, nominated "one of the best true-crime  podcasts at the British Podcast Awards 2018", and featuring 12 murderers, including 3 serial killers, across 15 locations, totaling 50 deaths, over just a one mile walk