by Jean Henry Mead
The rule of thumb in determining when a person dies is that the body begins to stiffen and rigor mortis sets in about two hours following death, according to Lee Lofland in his book, Police Procedurals & Investigations. The facial muscles move downward first, then the lower muscles of the body.
As rigor mortis sets in the body becomes stiffer until it’s completely rigid, which happens within eight to twelve hours. As soon as the heart stops pumping, gravity takes over and pulls the blood supply to the lowest parts of the body where the tissue takes on a purplish tint with the appearance of bruising. Laymen who find bodies often think the victim has been badly beaten, particularly if it’s found face down. The face will have also taken on the purplish hue.
Blood pooling reaches its peak within eight to twelve hours and deteriorating blood vessels cause blood to leak into surrounding tissue. Lividity, or discoloration of the skin, is set within six to eight hours and can shift from one area of the body to another if the body is moved, which indicates to investigators that the victim died in another location.
Body temperature is also an indication of time of death. The normal body temperature is about 98.6. When a person dies the body temperature drops 1.5 degrees per hour until it is the same as its surroundings. Therefore, if the victim is found in a room with a temperature of 75 degrees and the body registers 86.6, death occurred approximately eight hours earlier.
Variables occur if the victim is found in the snow or on ice. The body cools much quicker under those circumstances just as it would cool slower in a hot tub or on the desert. Investigators take careful note of the surroundings so that pathologists can factor in the circumstances when determining the time of death.