Algor Mortis and Rigor Mortis

Who are Algor and Rigor Mortis and Their Compatriot Entomology?

Algor mortis and rigor mortis are two elements used in estimating the approximate time of death.  Algor mortis refers to the cooling of the human body after death and rigor mortis refers to the stiffening or rigidity of the body due to the release of calcium and muscle contraction. In many fictional murder mystery books and television crime dramas, the reader or viewers are left with the impression that modern forensic science can determine the actual time of death.  While this makes for good entertainment, science isn’t quite that precise. Many things can be learned and concluded from algor, rigor, and livor mortis as well as stomach or intestine contents along with entomology; but the best that can be accomplished is an approximate estimation or window for the time of death.

Algor Mortis and Rigor Mortis

Many things can be learned and concluded from algor, rigor, and livor mortis as well as stomach or intestine contents along with entomology; but the best that can be accomplished is an approximate estimation or window for the time of death.

Algor Mortis 

The cooling of a human body is dependent upon several environmental factors.  If the body is found outdoors, is it covered with foliage, in a shaded area or exposed to direct sunlight?  Is the body clothed or naked?  If the body is found indoors is it clothed or not? Is it covered with blankets? What is the thermostat setting and does it adjust throughout the day?  All of these factors must be analyzed in estimating the approximate time of death.

The basic facts are the human body cools at the rate of approximately 1.5 degrees per hour in an ambient setting of seventy degrees for the first twelve hours after death, and approximately half of this rate thereafter until it reaches the ambient temperature.

Rigor Mortis

At the time of death, skeletal and cell activities cease to function, the body becomes locked in a set position and is unable to relax or move. Calcium leaks or is released from cell membranes and muscle fibers begin to contract.  Rigor begins to set into the smaller muscle groups first, within two hours and continues into the large muscle groups for up to twelve hours. Within approximately fifteen hours, muscle fibers break down and begin to soften until the stiffness gradually disappears.  Once again, environmental factors must be considered because heat accelerates rigor and cold retards its progression.  Within two days, generally, rigor has dissipated.  A common rule of thumb is rigor will not be noted within the first two hours after death or two days post death.

Entomology

Insect activity can begin immediately after death with the arrival of the blowfly eggs. They usually appear within the first eight hours in the warm moist body cavities, most notably the eyes, nasal passages and mouth of the corpse.  The eggs develop into the first stage larva within twenty hours and proceed to stage two around the two and a half day mark. By the fourth or fifth day, the larvae have progressed to stage three.  Somewhere between the eighth and twelfth day, the larva progresses to the pre-pupa. The pupa stage develops between day eighteen and twenty-one with the adult blowflies hatching around days twenty-one to twenty-four.

Next week we will tie everything together to demonstrate how the time of death window can be estimated with a fairly high degree of certainty.