The body of a person who dies goes into a state of rigor mortis within two to four hours. During this time, the chemical changes within the body cause the limbs and muscles to stiffen for up to four days. A cadaveric spasm, also called instant rigor, occurs post mortem in rare cases. A cadaveric spasm refers to the premature stiffening of a corpse before rigor mortis takes place. It is possible to mistake a cadaveric spasm for rigor mortis.
According to Pounder, you can establish the time of death using the rate method or the concurrence method. The rate method measures the changes that occur in a body after death. The concurrence method examines the details of the activity surrounding the death. The time on a watch that stopped working due to damage during a struggle, for example, can indicate the approximate time of death.
Look for and examine evidence found near or on the deceased’s body. Such evidence can include bodily injuries, anamnestic evidence and environmental evidence. Forensic scientists find anamnestic evidence based on an individual’s daily routines or habits. Environmental evidence refers to items found near a body, such as footprints or broken items.
Establish the current type of postmortem change in the body. According to Professor Derrick J. Pounder, head of the University of Dundee’s Department of Forensic Medicine, these changes include algor mortis, rigor mortis, livor mortis and postmortem decomposition, adipocere or mummification. Algor mortis refers to the gradual cooling of a dead body, before rigor mortis takes place. A cadaveric spasm always takes place before rigor mortis; therefore, a body past the rigor mortis state will not experience a cadaveric spasm.
Figure out the deceased’s body temperature to help establish the time of death. You may get the most accurate body temperature readings from a corpse via the rectum or by cutting a hole in the abdomen and placing a chemical thermometer in the opening. It is best to get a temperature reading as early as possible. The closer the temperature of a body is to the surrounding environment, the longer it has been dead. However, you must take into account factors such as layers of clothing, the temperature of the ground and humidity.
Learn the individual’s degree of activity before death. Pounder states that for reasons unknown, a body may experience a postmortem cadaveric spasm after an episode of violence or intense emotions. A dead body tightly gripping a weapon, a defense object or environmental items surrounding the body — like grass — can indicate a cadaveric spasm.
Notice the involuntary movements of the deceased’s body. Cadaveric spasms happen at the moment of death and persist through rigor mortis. In some instances, the body may appear to move or twitch as the muscles and joints begin to tighten during such a spasm, before rigor mortis. During this time, the muscles may tighten so much that it takes considerable force to move them or break a grip.