Rigor Mortis and Lividity are two natural occurrences within the human body after death that can be used as a means of determining – or at least estimating – when the deceased died.
What is Rigor Mortis?
Rigor Mortis is the stiffening of the body after death because of a loss of Adenosine Triphosphate (ATP) from the body’s muscles. ATP is the substance that allows energy to flow to the muscles and help them work and without this the muscles become stiff and inflexible.
Rigor Mortis begins throughout the body at the same time but the body’s smaller muscles – such as those in the face, neck, arms and shoulders – are affected first and then the subsequent muscles throughout the rest of the body; those which are larger in size, are affected later.
Rigor normally appears within the body around two hours after the deceased has passed away with – as we have already mentioned – the facial and upper neck and shoulder muscles first to visibly suffer from its effects. Many Scenes of Crime Officers (SOCO) have reported that upon discovering the deceased that their face might have taken on what looks to be a grimace; this is because the facial muscles have contracted as ATP drains from them.
Once the contracting of all the body’s muscles has taken place this state of Rigor – technically referred to as the Rigid Stage – normally lasts anything from eight to twelve hours after which time the body is completely stiff; this fixed state lasts for up to another eighteen hours.
Contrary to common perception the process of Rigor Mortis actually does reverse and the body returns to a flaccid state; the muscles losing their tightness in the reverse of how they gained it: i.e.: those larger muscles that contracted last will lose their stiffness first and return to their pre-Rigor condition.
Rigor Mortis is a good means of indicating time of death as is normally visible within the first thirty-six to forty-eight hours after death; after which it leaves the body.
What is Lividity?
Lividity is also useful for this purpose. Lividity is the process through which the body’s blood supply will stop moving after the heart has stopped pumping it around the inside of the deceased. What normally happens at this point is that the blood supply – or at least any blood that remains within the corpse depending on the nature of their death – will settle in direct response to gravity. For example an individual found lying on their stomach would be found with all the blood from their back heading towards the ground. Lividity also displays itself as a dark purple discolouration of the body and can also be referred to as Livor Mortis or Post Mortem Hypostasis.
Any part of the body which has come into contact with a firm surface for a period of time – such as a floor or bench top – will show signs of this during lividity as this impression against the skin displays itself as an indentation surrounded by gravity-pulled blood.
It is worth noting that lividity begins to work through the deceased within thirty minutes of their heart stopping and can last up to twelve hours. Only up to the first six hours of death can lividity be altered by moving the body. After the six hour mark lividity is fixed as blood vessels begin to break down within the body. Rigor mortis and lividity are some of the key factors that are used when Estimating the Time of Death.