FREE online courses on the Basics to Forensic Entomology - DEAD What happens after that - Rigor mortis

 

Rigor mortis is a well known phenomenon, and is due to a complex chemical reaction in the body. In the living body muscles can function both aerobic and anaerobic. In the dead body muscle cells can only function anaerobically. When muscle cells work anaerobically the end product is lactic acid. In the living body, lactic acid can be converted back, by means of excessive oxygen uptake after an anaerobic exercise. In the dead body this cannot happen, and the breakdown of glycogen in the muscles leads irreversibly to high levels of lactic acid in the muscles. This leads to a complex reaction where actin and myosin fuses to form a gel. This gel is responsible for the stiffness felt in the body. This stiffness will not be over before decomposition begins.

As rigor mortis is due to a chemical reaction, the reaction time is due to temperature and the initial concentrations of lactic acid. High metabolic activity in the time just before death, for example when running, leads to higher levels of lactic acid, and shorter time for the rigor mortis to develop. Higher environmental temperature also leads to a shorter reaction time.

 

In temperate regions the following rules of thumb can be used in estimating death, but must be used with caution:

 

Temperature of body	Stiffness of body	Time since death
Warm	Not stiff	Not dead more than three hours
Warm	Stiff	Dead between 3 to 8 hours
Cold	Stiff	Dead between 8 to 36 hours
Cold	Not stiff	Dead in more than 36 hours

 

Rigor mortis should never be the only basis for estimating time of death.

 

After death, a lot of internal organisms in the intestine will become very active. Escherishia coli and others will start multiplying, and the decomposition begins. First the intestine and the blood will be attacked, and when gas formation and other things lead to rupture of the intestine other organs will be attacked. Organs start decomposing at different times after death, and may also be used in estimating time of death.

 

The decomposition of a body can be divided into several stages, even if the duration of each stage will vary a lot:

 

Stage	Description
Initial Decay	The cadaver appears fresh externally but is decomposing internally due to the activities of bacteria, protozoa and nematodes present in the animal before death
Putrefaction	The cadaver is swollen by gas produces internally, accompanied by odor of decaying flesh
Black putrefaction	Flesh of creamy consistence with exposed parts black. Body collapses as gases escapes. Odor of decay very strong
Butyric fermentation	Cadaver drying out. Some flesh remains at first, and cheesy odor develops. Ventral surface moldy from fermentation
Dry decay	Cadaver almost dry; slow rate of decay

 

In the rest of this course we will focus on the telltale signs that insects can provide in the investigation of suspicious deaths.