1. Muscles begin to stiffen within 1 to 3 hours after death at 70 to 75°F.
2. A high fever or high environmental temperature will cause rigor to occur sooner.
3. Rigor will occur more quickly if the decedent was involved in strenuous physical activity just before death.
4. All the muscles begin to stiffen at the same time. Muscle groups, because of their different sizes, appear to stiffen at different rates. Stiffness is apparent sooner in the jaw than in the knees. The examiner must check the jaw, then the arms, and finally the legs, to feel if the associated joints are moveable.
5. The body is said to be in complete rigor when the jaw, elbow, and knee joints are immovable. This takes approximately 10 to 12 hours at 70 to 75°F environmental temperature.
6. The body will remain stiff for 24 to 36 hours at 70-75 degrees F before the muscles begin to loosen, usually in the same order they stiffened.
7. Rigor is retarded in cooler temperatures and accelerated in warmer temperatures.
8. When the body stiffens it remains in that position until the rigor passes or the joint is physically moved and the rigor is broken.
9. The position of a body in full rigor can give an indication whether or not a body has been moved after death.
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