DEPARTMENT OF ANATOMICAL SCIENCES
AN321 - FORENSIC OSTEOLOGY
TIME SINCE DEATH
W. B. Wood
The University of Queensland
It is important for the forensic pathologist or osteologist to provide some estimate of the time since death of unidentified human remains so that the police have some guidance as to when the person may have died or gone missing and been reported to the Missing Persons Bureau.
Crucial to such a determination is evidence derived directly from the remains as well as evidence from the recovery scene. Important details include the location and disposition of the remains, whether open & exposed or contained within an enclosed space, clothed or unclothed, wrapped, on the surface, underwater, buried (and depth of burial), shaded or in sunlight, ambient temperature, rainfall, vegetation, soil type, evidence of carnivours or rodents (droppings, tracks) and whether the remains are compact or scattered,etc.
The rate of decomposition is greatly accelerated by antemortem trauma, the action of predatory carnivours and rodents, access to insects, and particularly by high temperature and humidity. A recent report from Florida USA stated that complete skeletonisation had been observed to occur in as little as 3-4 days after a body had been placed in a dump and covered by a vinyl sofa in the middle of summer.
In relatively recent death, evidence as to the time of death may be provided by the degree of postmortem cooling of a body, and depends on the ambient temperature, the presence or absence of clothing, and the degree of obesity etc. As a rule of thumb, the body cools 1 1/2 degrees F per hour.
Livor Mortis & Rigor Mortis:
The presence of livor mortis and of rigor mortis also provide evidence of relatively recent demise.
Livor mortis development begins immediately after death but does not become apparent until about 2 hours after death. It reaches its maximum after 8-12 hours and after that time becomes fixed. During its development phase it distribution may still change if the body is shifted. After 12 hours, any movement or relocation of the body will not affect the distribution of the lividity ie it has become fixed in position.
Rigor usually develops 2-4 hours after death and gradually disappears after 36-48hours. The onset and duration is dependent on the ambient temperature and the amount of oxygen debt of the muscles immediately prior to death. Rigor mortis may appear almost immediately after death and disappear within 9-12 hours in extremely hot environments or if the subject was suffering from a generalised bacterial infection prior to death. Similarly its onset and departure may be delayed in rapid cooling or freezing of the body after death.
The chemical constituents of the Vitreous Humor of the eye especially the potassium level increase after death and have been used to estimate the time interval since death.
Physical Examination of Remains
The rate and type of decomposition that is observed in a body also provides evidence as to the time of death. However it is extremely sensitive to a variety of intrinsic and environmental influences (Mann RW et al 1990)
the physical state of the body at the time of death
thin and emaciated - skeletonise faster
well nourished - form adipocere
the presence of antemortem trauma
the prevailing temperature and humidity
the postmortem interval before burial (if buried)
the influence of clothing
the influence of any other wrapping material (plastic, blankets etc)
the depth of interment (in the case of burials)
soil type and pH
the presence of decaying vegetable matter
access to insects
the influence of scavengers eg dogs, rodents, foxes, wild pigs etc
The following features should be carefully noted in skeletonised remains:
remnants of soft tissue:
muscles, ligaments, tendons, cartilage
mummified soft tissue
hair & fingernails
bone odour (putrefaction) & a greasy feel
weathering - bleaching, surface flaking & cracking, chalkiness
bone erosion - due to wind, sand, soil or water abrasion etc
bone invasion by termites, rootlets
bone surface colonisation by marine organisms (bryazoa, tubeworms, barnacles
rock boring sponges etc.)
surface algae or mould
In the case of skeletal remains found on the surface, the presence of putrefaction odour and a greasy feel of the bones indicates relatively recent death, probably less than one year. For buried remains these signs may persist for up to 5 years.
Evidence of weathering (ie bleaching, surface cracking and flaking, and the development of a chalky appearance) usually takes two to five years to develop in bones exposed on the surface.
Extensive scattering of skeletal remains (due to scavengers) usually takes some years to occur.
Buried skeletons in a soil environment of pH <6 and with constant percolating groundwater may completely disintegrate in about 5 years.
Chemical Examination of the Bones
Changes in the organic constituents of the bones have been reported as being useful in the determination of the time since death. The following organic methods are probably the most useful but still have to be proven reliable in their application to actual cases (Knight & Lauder 1969, Facchini & Pettener 1977):
a) The benzedine test
if positive then probably < 150 years
b) Ultraviolet fluorescence
if universally present then probably < 100 years
c) The number of aminoacids in bone hydrolysate
if > 7 then probably < 100 years
d) Bone nitrogen level
if > 3.5g% then probably < 50 years
e) The presence of prolines
if present then probably < 50 years
f) Antihuman serum reaction
if +ve then probably < 5 years
Examination of Associated Artifacts
Condition (and possible dates) of:
clothing: types, material, quality, colour, buttons
jewellery: finger rings, ear-rings, necklaces, brooches, bracelets
glasses: type (bifocals etc), frame type
dentures: upper, lower, partial, complete, composite material, ID number
leather: belts, handbags, shoes, wallets,
paper: banknotes, newspapers, licences, receipts, tickets
metal objects: buckles, penknives, zips, coins
Examination of environmental evidence
insects: fly maggots (stage of development) & pupae
beetles, termites etc
vegetation: root invasion of bones
growth or regrowth of damaged grass, shrubs etc
soil: buildup, erosion, settlement in a grave, etc
weathering: bleaching of bones, surface flaking of
animal activity: evidence of bone scattering,
products of decomposition:
volatile fatty acid concentration within the underlying soil
Much research still needs to be done to refine methods of estimating time since death. At the moment, most estimates are still only educated guesses.
Facchini F & D Patternur 1977 "Chemical and physical methods in dating human skeleton remains." AJPA 47:65-70
Knight B & I Lauder 1969 "Methods of dating skeletal remains." Human Biol. 41:322-341
Mann RW, Bass WM & L Meadows 1990 "Time since death and decomposition of the human body: variables and observations in case and experimental field studies." JFS 35(1):103-111
Smith KGV 1986 A Manual of Forensic Entomology. British Museum of Natural History London