Estimating Time Since Death
Terms in this set (96)
Postmortem Interval (pmi)
is the time since death- the period of time when death occurred to when the body is recovered.
Importance of knowing tsd?
1. establishes time frame (differentiate between antemortem, perimortem and postmortem), 2. ID - to narrow number of missing individuals. 3. verify or refute alibis.
Time before death
study of the stages of human decomposition, both the intrinsic factors (body) and extrinsic factors (how environmental factors affect decomp)
study of insect life and succession on cadavers to help estimate time since death
study of plant life/growth to help determine postmortem interval
What's also good to notice on a decomposing body?
State of deterioration on textiles and money
Stages of Decomposition
Fresh, Early Decomposition (bloat), Active decay, Advanced decay, Skeletal/dry remains, and Extreme decomp.
Variations of Decomposition?
Generally the stages of decomp follows the systematic pattern however variations occur to the fact that the rate of these stages varies thus stages could overlap and also different stages could occur at different parts of the body depending on their conditions and how they were "buried"
Size of body, Presence and type of perimortem trauma, Diseases
Are the injuries to the body that occurred during death- usually could be the cause of death. For example: gaping wound from a bullet
temperature, depositional environment, humidity, sun exposure, clothing/body covering, animal scavenging, insect colonizing.
Stages of Fresh Decomp
Pallor mortis, Algor mortis, Liver mortis and Rigor mortis
"paleness of death" - causes skin to go pale due to lack of blood circulation. Lack of oxygen to cells = cell death
When can Pallor mortis be used for tsd?
Only if the body has been found w/in 30 minutes of death
How long for brain cells to die due to lack of oxygen? Skin cells?
Brain cells: 3-7 minutes. Skin cells = 24 hours
"Coldness of death" - postmortem cooling- body cools about 1.5 F/hour until it reaches ambient temp.
Assumed normal core body temp?
98.4 F or 36.9 C
Rough Calculations for tsd
98.4 F - (rectal temp) x (2/3)
36.9 C - (rectal temp) x (6/5)
Assumptions made for determining tsd for algor mortis?
Normal Body temp, Body cooling constant, Environmental conditions did not change.
Normal Body temp
ranges from 92-101 F (32.2-38.2 C) depending on which body cavity was measured
Factors affecting algor mortis
ambient temp, clothing condition, air movement, size of individual
"blu-ish colour of death" - lividity and hypostasis - the settling of blood via gravity (blood pooling) - results in reddish/purple coloring of skin.
What parts of the body are unaffected by livor mortis?
parts of the body in contact with the ground or objects -due to the fact that capillaries are crushed (contact pallor)
When is the livor mortis fixed?
8-12 hours in room temperature condition.
What can liver mortis help tell (besides tsd)?
once blood has been fixed it won't change even if the body position has been changed and so can tell if body has been moved.
"stiffness of death" - progressive hardening of muscles due to chemical changes in the muscle fibers
Rigor mortis process
happens soon after death affecting small muscles of hands and face first (2-4 h), then affects larger muscles after 12h - then recedes after 24h of death because of cellular decomp - disappearing in reverse order of appearance
What else can rigor mortis do?
can cause stiffening of arrector pilli muscles in skin resulting in "goose pimples"- and can cause hairs to stand on end.
How can you undo rigor mortis?
Muscle rigor mortis can be broken down with forceful manipulation and will not re-occur.
Rigor mortis timing is affected by?
body size, internal body temp, ambient temp, individual's muscle mass and physical activity before death
early rigor mortis (antemortem) due to extranneous excercise just before death. .
tsd if body is warm and not stiff? warm but stiff?
warm and not stiff = less than 3 hours
warm and stiff = 3-8 hours
tsd if body is cold and stiff? cold but not stiff?
cold and stiff= 8-30 hours
cold and not stiff = more than 30 hours
if eyes are partially open after death - drying may cause a horizontal bloody line across the eye where the eyelids meet.
Postmortem drying of mucous membranes can cause...
the darkening of tissues such as around the lips and tongue.
"self-digestion" - digestive enzymes from the intestinal tract digest the body like food - degeneration of body tissues.
during "fresh" stage of decomp.
decomp caused by proliferating bacteria in the body - they eat away body tissue and produce gases at the body cavities =bloat.
Early decomposition sign
24-36 hours after death - lower, right of abdomen where the cecum is located turns green -b/c its filled with bacteria
Marbling (early decomp)
delineating of blood vessels = they become very prominent
subcutaneous build up of gas (due to bacteria) occurs 36-72 hours postmortem - mainly the abdominal cavity, scrotum, face and neck.
smelly, red-brown fluid that leaks out of body cavities (oral, nasal and pelvic) about 3 days to a week postmortem
gases within stomach expand causing the "last meal" to rise up esophagus and out of mouth. Can occur before Purge fluids
comes from the lungs
Why does the body turn greenish-black in early decomp?
Gases (from bacteria) are continually being produced in cavities and organs causing the discoloration
is the peeling of skin (gloving = hand) - caused by autolysis and resulting fluids cause the epidermis to separate from dermis. Occurs 4-7 days postmortem
Black Putrefaction and Soft Tissue decay
10-25 days postmortem - autolysis and putrefaction continue - corpse turns black and reeks of "smell of death" - bloating desists (body flattens out) and skin peels back (easy access for insects)
Smell of Death
hydrogen sulfide, cadaverine, putrescine and methane.
Order of soft tissue decay
1. GI tract and circulatory system 2.air passages and lungs 3.kidneys and bladder 4. brain and nervous tissue 5.skeletal muscles 6. Connective tissue
Butyric Fermentation, Mummification, Adipocere,
body finishes flattening out and fluids continue to slowly dry up. happens 20-50 days postmortem,
produces distinct cheesy smell - it is a component in the breaking down of body fluids
may or may not happen - requires warm and dry environment - body dries out halting body decomp and bacterial activity, skin becomes dark and leathery and organs deteriorate and have putty like consistency. can be only one or few parts of body
Full mummification occurs...
in optimum conditions can happen within a week but on average it usually takes 6 months
grave wax - no insect exposure, moist anaerobic (no oxygen) environment submersion of water, saponification occurs, bodu starts to resist bacteria and stops decomp.
is the hydrolysis of fats into fatty acids and soaps because of bacterial enzymes - most evident in butt, cheeks, stomach and breasts
Full adipocere occurs...
can occur in a month but usually takes more than a few months, with higher fat content it is more likely to occur, can keep the body preserved for years
body reduced to skeletons - with some soft tissue (most are within the soil/environment -if not the body has been moved). usually occurs more than 50 days later, but highly depends on environment.
Skeletonization caused by bleaching and exfoliation
loss of long bone epiphyses and metaphyses which exposes spongy bones
Temperature affects decomp
warmer temperatures = faster decomp
decomp faster in sun than shade
cycle of thaw and cool speed decomp
Humidity affects decomp
higher humidity faster decomp
Forensic entomology can help determine
1) estimate tsp using the various insects on the dead body
2) season of death
3) geographic location
4) personal habits
occurs within minutes (sometimes even sooner) on an body - they come even faster when open wounds are present
7 natural openings of the body
mouth, nose, ears, anus, vagina, eyes, urethra
What are the two major insect groups associated with cadavers?
flies and beetles
Name 4 fly species associated with cadavers
Blowflies, Flesh flies, House flies, Cheese skippers
Name Beetle species on cadavers
carrion beetles (silphids, hister, sap and rove)
hide and ham beetles,
Order of types of insects that appear on the body
necrophages, omnivores, parasites and predators, and incidentals
are the first species that are attracted to corpses and feed on corpse tissue (flies and beetles)
ants, wasps, and beetles that feed on corpse as well as maggots
predators and parasites
beetles and flies and wasps that parasitize the maggots - eat them and use them to lay their eggs
bugs, spiders, mites and centipedes that don't normally feed on decaying flesh but it happens to intrude into their environment so they make use of it
Which insect life cycle is important in the early stages?
Blowfly life stages
Eggs (24h)--> Larvae 1 (27h)--> Larvae 2 (22h) --> Larvae 3 (130h) --> Pupa (143h) --> adult
at around 70 degrees F
Blowfly eggs look like? maggots? pupae?
Eggs = uncooked tiny white rice
Maggots = cooked rice
Pupae = cooked brown rice
Fresh stage: ants and roaches like to...
crawl on the cadaver and their activities leave marks on the cadaver that look very much like abrasions
Maggot activity during early decomp
young maggots move throughout body devouring the soft tissue -spreading bacteria and secreting digestive enzymes
-they move in masses increasing the rate of decay as well as increasing odour which attracts other bugs to both feed on maggots and cadaver
Maggot activity during active decay
there are plenty of generations of maggots at this time now. Mature maggots also have started to migrate away from the body and bury into the nearby soil so as to mature into pupae
Insect activity in active decay
more predatory and parasitic action - predatory maggots and parasitic wasps are more prevelent, "pioneer flies" retreat, and beetles start to lay their eggs hatching and then feeding on the flesh
Maggot activity in advanced decay
its starting to slow down because there is less soft tissue on the body now which is less desireable to maggots
but this is when cheese flies are more prevelent where they feed off the remaining soft tissue
Insect activity during skeletal /dry remains stage
dermistid beetles, moths and bacteria feed on keratin and hair. Mites feed on the bacteria
Collecting samples of insects
-take the largest maggots on body (most mature)
-get representatives of other maggots present
-preserve some maggots in alcohol, and rear the others to confirm species ID
Why is it important to know temperature history?
Exact temperature history and the weather allows to provide info on how the environment was like when the person died, and helps to figure out what the insect activity was like (whether it would help increase decay or decrease decay)
Determine TSD with insect activity
1. collect samples of insects
2. temperature history at crime scene
3. estimate time of egg laying
4. other insect evidence available? (that might contradict original estimated tsd)
Canada's only full-time forensic entomologist?
Dr. Gail Anderson
medico-legal study of plants associated with cadavers
Botanical evidence can?
-determine circumstances and sometimes COD
-establish place of death
-determine if there were multiple crime scenes
-prove or disprove alibis
-place a suspect at a crime scene.
What does it mean if diatoms are found in the stomach? in the lungs? in the blood?
stomach - water swallowed
lungs - aspirated water in
blood - water was aspirated while victim was alive
How to use plants for determining TSD?
-examine amount of plants in, under &over human remains
-count growth rings
-presence of seasonal pollen
counting number of growth rings in roots, stems and tree trunks (1 growth ring = 1 year of growth)
Limitations of forensic botany
-plants near remains grown after body deposited can only give minimum tsd
-b/c growth rings take 1yr to develop and so can't be used to determins tsd with individuals dead for <1 year
Deterioration rate of textiles and money
plant-based textiles decay fastest (cotton, flax, jute, hemp)
chemical based textiles decay next (acrylics, acetate, rayon, polyester)
animal based textiles preserve very well (esp. silk and wool)