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Time of death

Time of death

Posted By IFS

After a person dies there will be certain changes in the body. Because there is no heartbeat and therefore no blood flow, the blood still present in the vessels will descend under the influence of gravity to the lowest point in the body. The discolorations that are produced by this process is known as livor (postmortem lividity). Soon after a person has died, heavy red blood cells descend to the lowest parts of the body. In the early stages of death, it is possible to press the postmortem lividity away, with finger pressure. After some time the postmortem lividity remains fixed and can be used to make time of death determinations. However, there is a considerable variation in the number of hours in which both postmortem lividity and fixation can occur. This makes this method unfit to establish an accurate time of death.

Time of death

Another change that will occur in the body after death, is a condition known as rigor mortis. This is stiffening of the muscles. Here too there is a wide variation in time of occurrence and the degree and duration in which the rigor mortis persists. Therefore this method is also unfit for an accurate determination of the time since death, also known as postmortem interval (PMI). If the data about postmortem lividity and rigor mortis can be used in combination with other methods, that data can provide valuable information.

However, the cooling rate of the body after death offers the best indication to determine the PMI.

The most comprehensive method is “the rule of thumb”. Here, an average cooling rate of the body of 1 degree Celsius per hour is presumed. However, there are many factors that have an influence on the cooling rate. So that is why also “the rule of thumb” method is unfit.

Scientific research into the cooling rate of the body has produced two models that are used in the Netherlands: Henssge’s nomogram and the calculation model according to TNO.

Both models use mathematical formulas to calculate a time of death, with a certain time period (spread), in which the death may have occurred. This is the uncertainty interval. In Hennsge’s nomogram it is a minimum of three hours before and three hours after the calculated time, (a postmortem interval of at least 6 hours). In the model of TNO it is dependent on the available data.