A police detective working out of homicide is called to an apparent murder scene

Question

A police detective working out of homicide is called to an apparent murder scene. In the victim's hand is a slip of paper which is presumed to be important However, the paper is gripped so tightly that the detective cannot pry the fingers apart to get at it How can it be that a dead body can hold onto a piece of paper and more tightly than was possible for that individual when she was alive? Does this situation provide any evidence concerning the time of death, and if so, what can be deduced about the timing?

Explanation / Answer

A few hours after a person or animal dies, the joints of the body stiffen and become locked in place. This stiffening is called rigor mortis. Rigor mortis can be used to help estimate time of death. The onset of rigor mortis may range from 10 minutes to several hours, depending on factors including temperature (rapid cooling of a body can inhibit rigor mortis, but it occurs upon thawing). Maximum stiffness is reached around 12-24 hours post mortem and rigor mortis lasts approximately 72 hours. Rigor mortis is a phenomenon caused by the skeletal muscles partially contracting. The muscles are unable to relax, so the joints become fixed in place. Living muscle cells expend energy to transport calcium ions to the outside of the cells. The calcium ions that flow into the muscle cells promote the cross-bridge attachment between actin and myosin, two types of fibers that work together in muscle contraction. The muscle fibers ratchet shorter and shorter until they are fully contracted or as long as the neurotransmitter acetylcholine and the energy molecule adenosine triphosphate (ATP) are present. However, muscles need ATP in order to release from a contracted state (it is used to pump the calcium out of the cells so the fibers can unlatch from each other). ATP reserves are quickly exhausted from the muscle contraction and other cellular processes. This means that the actin and myosin fibers will remain linked until the muscles themselves start to decompose.

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