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Time of Death

IntroductionEstablishing the time of death or the interval between the time of death andwhen a body is found (postmortem interval) typically cannot be determinedwith certainty. Unless death is witnessed, the exact time of death cannot bedetermined; however, sucient information is often available to allow estimationof a range of time encompassing the actual moment of death. ngeneral, the shorter the postmortem interval, the narrower the estimatedtime range. !onversely, a longer postmortem interval entails a broader rangeestimate and often a greater chance for error. "o single observation about adead body is a reliable or accurate indicator of the postmortem interval.

#he most reliable estimates are based upon a combination of numerousobservations made of the body and the scene of death. $bserved conditionsinvolving the body include rigor mortis, livor mortis, algor mortis anddecomposition. #he stomach contents may also help in determining the timeof death. n addition to examining the body, it is also important to investigatethe scene of death, during which time the environmental conditions shouldbe documented. Environmental conditions, especially the temperature, arethe most important factors a%ecting the changes the body undergoes afterdeath. $bservations made during the scene investigation help assess the bodychanges and may also o%er additional information useful in estimating whendeath occurred. #he combination of scene and body examinations will givethe investigator the best chance of reliably estimating when death occurred.

and experience in death investigation as soon as possible after the bodyis found. #he body should not be unnecessarily manipulated prior to ma&ingthese observations. !hanges in the environment, such as opening doors andwindows or turning on air conditioning, should also be minimi'ed until theobservations are made.

Rigor Mortis#he muscles of the body initially become accid after death. ithin *+ hoursfollowing death, the muscles begin to become noticeably increasingly rigid andthe -oints immobile (free'e) due to a process &nown as rigor mortis (postmortemrigidity, rigor). #he chemical processes causing the muscles to sti%en arenot clearly understood but are similar, although not identical, to physiologicmuscle contraction in that both of these processes involve calcium and#/01/. 2igor mortis involves the formation of loc&ing chemical bridgesbetween the muscle proteins actin and myosin and does not involve muscularshortening, while physiologic muscular contraction involves shortening ofmuscle as the actin molecules reversibly slide over the myosin molecules.hen a body sti%ens, it remains in that position until rigor passes or itis physically overcome (bro&en), such as when a -oint is forcibly moved. 3incethe chemical process of rigor is irreversible, fully developed rigor will notrecur in an area in which it has been bro&en or in an area in which it hasalready passed. 4owever, if rigor is overcome prior to its full developmentthe process will continue to completion, resulting in the apparent recurrenceof rigor in that area, albeit to less than expected 5full6 sti%ness.ll muscles of the body begin to sti%en at the same time after death.

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4owever, the sti%ening becomes noticeable in the smaller muscle groupsbefore the larger groups, giving the appearance that rigor mortis proceeds atdi%erent rates in the various muscle groups. 3ti%ness is usually apparent 7rstin the -aw, then the elbows and 7nally the &nees. body is said to be incomplete or full rigor when the -aw, elbow and &nee -oints are immovable.

#he ability to passively move a -oint is dependent on the amount of muscle

controlling the -oint. 2igor involving a -oint with a small amount of musclesuch as the 7nger is easily overcome, while it may be dicult to move a -ointsuch as the elbow, which is connected to relatively large muscles. s a rule,men will have stronger rigor than women since men typically have a largermuscle mass than women. 8arge muscles, especially in muscular individuals,may become so resistant to stretching that it may re9uire the e%orts of morethan one person to move a large -oint. $ccasionally, the bone may brea&before the rigor mortis is overcome. !onversely, rigor may be poorly formedor not apparent in individuals with little muscle mass, such as infants or emaciated

adults.

!omplete rigor ta&es approximately *:+* hours to fully develop in anaverage si'e adult when the environmental temperature is

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prior to death. t has also been associated with some other circumstancessuch as electrocution.n contrast to elevated environmental temperature, cold conditions mayretard or prevent rigor mortis. #he process will begin or accelerate when thebody is allowed to warm. f a body is not in complete rigor and is placed inrefrigeration the process will slow down and may stop. 2igor may proceed

to completion when the body is warmed. #he sti%ness of rigor must bedi%erentiated from muscle hardening or free'ing due to very cold weather.Under such environmental conditions, rigor may be dicult to evaluate.

2igor mortis will also aid the investigator in determining if the body hasbeen moved. f an investigator arrives on the scene and 7nds an unsupportedarm or leg stic&ing up in the air, the investigator &nows the decedent hasbeen moved after rigor has set in. person may die with the arms or legs inthe air, but gravity will prevent the unsupported extremities from remainingthere after death.

Livor Mortis

8ivor mortis (postmortem hypostasis, lividity) is the discoloration of thebody after death due to the gravitational settling of blood which is no longerbeing pumped through the body by the heart.8ivor mortis is usually noticeable approximately * hour after death andis often apparent earlier, within :+: minutes. #he discoloration increasesin intensity and usually becomes 57xed6 in about C+*: hours; however, thetime interval to 7xation is unpredictable and may be signi7cantly longer or,occasionally, shorter than the 5typical6 C+*: hours. /rior to 7xation, the bodycan be moved many times and the blood will resettle each time into thedependent areas. 4owever, after 7xation, the blood will remain where it hasalready settled even if the body is repositioned. ?ixation is a progressiveprocess that is not all or nothing. #hus, if a body with some 7xed livor is

moved, there may be some blood that is not 7xed and which is able to resettle.n such a case, discoloration will be seen in the repositioned dependent areasas well as in the original dependent areas. #he intensity of the livor in eacharea will depend on the extent of 7xation when the body was moved. /atternsof livor mortis in nonDdependent areas indicate the body or body part hasbeen moved after death. ndividuals dying of some natural diseases, ofteninvolving terminal congestive heart failure, may have intense congestion ofthe head, nec&, shoulders and upper chest, resulting in discoloration of theseareas that appears to be similar to livor mortis except that it is not con7nedto dependent areas. 3imilar discoloration may also be seen in some cases ofmechanical asphyxia. 1iscoloration due to blood congesting vessels that isnot related to gravitational settling needs to be di%erentiated from livor

mortis. 2arely, 5lividity6 has been observed in living people who have severecardiovascular disturbances such as congestive heart failure.

#he formation of livor may be hindered or prevented by pressure appliedto the bodyBs surface because the small blood vessels become compressed andblood is prevented from settling into them. ?or example, if a body is lyingon its bac&, pale areas will typically be found over the scapulae, buttoc&s andcalves. n addition, any ob-ect pressing against the s&in with sucient pressureto compress small blood vessels will be prevent blood from draining

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into them. /ale mar&s within 'ones of livor mortis may be caused by tightclothing (bra, underpants, belts), surface irregularities (wrin&led clothing or bedding) or ob-ects abutting the surface (coins in a poc&et, marble on theoor). #hese patterns enable the investigator to -udge if the body has beenmoved and to help in reconstructing the bodyBs previous position.8ividity tends to be violaceous or purple in a lightDs&inned individual

and dar&er in someone with dar&er s&in. 8ivor may not be apparent in adar&ly pigmented person. /eople who die from extensive blood loss or whowere severely anemic may have light or no apparent livor due to the smallamount of blood or hemoglobin in their vascular system.n certain causes of death, livor mortis may ta&e on a di%erent color.!arbon monoxide poisoning, cyanide poisoning and hypothermia are oftenassociated with livor mortis that appears bright red or pin&. 3imilar colorationof the livor may be induced during refrigeration of the body. t iscommon to see red edges outlining the typical purple livor mortis at the timeof autopsy in a body that has been in the morgueBs refrigerator overnight.$ccasionally, most often in infants, the livor may be entirely red after thebody has been in the morgue cooler overnight. rown lividity has been

described in deaths caused by potassium chlorate and in deaths caused bynitroben'ene poisoning.8ivor mortis will be visible until the body becomes discolored duringdecomposition. !olor changes due to decomposition vary and include combinationsof red, green, brown and blac&. #he decompositionDinducedchanges will obscure the livor pattern and interfere with its interpretation.

#he examiner may not be able to determine whether the livor mortis is onthe bac& or the front of the body if decomposition is suciently advanced.n some cases, it may be dicult to distinguish livor mortis from contusion.n other cases, livor mortis may obscure the presence of contusion.n incision into an area of lividity will demonstrate blood con7ned to bloodvessels, whereas an area of contusion will have extravasated blood within the

soft tissues. 1ecomposition may add further diculty in recogni'ing contusionsand distinguishing them from livor mortis.$ccasionally, small blood vessels engorged with settled blood may passivelyrupture, allowing the blood to seep out of the vessel and create smallareas of 5hemorrhage.6 #hese extravasations, called #ardieu spots, are particularlycommon in distal extremities of hanging victims and generallymeasure less than 0*A in diameter. #hey can also be present in any part ofthe body which is in a dependent position for many hours, especially -ustprior to the onset of decomposition as the blood vessels lose their structuralintegrity and lea&. #hey should not be mista&en for the smaller pinpointhemorrhages called petechiae. /etechiae may occur when death is accompaniedby a sudden increase in venous pressure such as the terminal onset ofprofound heart failure or in asphyxial deaths involving compression of thechest or -ugular veins as may occur in compression asphyxia or manual strangulation. /etechiae are often seen on the face, especially on and aroundthe eyes. f a person lies face down and is in this position for many hours ordays, blood may accumulate in the small blood vessels of the eyes and orbit,resulting in a hemorrhagic or bloody appearance (5raccoon6 eyes) that mayfalsely suggest the presence of trauma. #he red0brown drying artifact of thecon-unctivae (tache noire de sclerotic) which occurs when the eyes are partially

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open after death also should not be confused with livor mortis.