SLE356 - Advanced Topics in Forensic Biology

Antemortem

before death

Postmortem

after death

Perimortem

in or around time of death

Postmortem interval (PMI)

the period of time between time of death and discovery

When does decomposition begin

as soon as the death occurs

Taphonomy

The study of decompostion and what happens to a person after they die

Stages of decomposition

Fresh, Putrefaction, Putrid Dry Remains

Active decompositon

bloat, putrefaction, decay

Advanced decomposition

skeletal remains

Algor mortis

Algor mortis or the coldness of death is a drop in temp caused by the lack of blood movement. It was previously used to determine PMI however it has proven to be unreliable and has the high potential for contamination

Livor Mortis

Livor Mortis also know as hypostasis or postmortem lividity is blood settling in the capillaries and veins of dependent parts of a body. It typically occurs 20-120 minutes after death.

Rigor mortis

Rigor mortis or muscle stiffening occurs in a 2-12 hour window (influence by environment) where the muscles start to contract in phases of relaxing and resetting. It starts in smaller muscles of face and those most used prior to death first, for example if they used alot of muscle right before death then those muscles would contract first. It is temperature dependent.

Cadaveric rigidity

• Muscle stiffening (in some or all of the body) immediately after death

• Seen in people who die in a state of extreme emotional/physical stress

Heat stiffiening

Pugilistic pose caused by exposure to extreme heat

Autolysis

Enzymes digesting cells

Bloat

Skin retains gasses and swells, it is causesd by autolysis

Putrefactive rigor

Build up of gasses in body - individual in ‘hug’ pose

Putrefaction

Soft body parts disappear form autolysis (enzymes digesting cells), microbial, insect, and animal activity

Skin slippage

Occurs in moist or wet habitats the epidermis begins to separate from underlying dermis

‘glove formation’ - when the skin separates as a relatively complete unit

Can be used for fingerprinting

Adipocere

Also known as Corpse or grave wax it is whitish, greyish, yellowish and has a soapy feel. It is caused by the breakdown of lipids and bacterial decomposition of triglycerides which produce glycerol and fatty acids and can preserve body when it is in large amounts as the lower pH slows decompostition. The odour is used to train cadaver dogs and it is most likely to occur on bodies that have been submerged, buried, sealed in containers or in peatbogs. Development is based on lipid content as well as clothing and surrounding however the rate of formation and agreement on conditions is not clear although moisture is key.

Mummification

Different from process to preserve tissue (egypt etc)

Results from exposure to dry and hot condditions

Skin becomes leathery

Common is australia

not much soft tissue left

Putris Dry Remains

Advanced stage

Gradual loss of soft tissue resulting in skeletonizarion (or in Australia, mummification)

Decay proceed more slowly

Uterus and prostate glands are fairly resistant to decay and could last for several months (in a well-sealed container)

Skeleton becomes disarticulated (nothing holding the bones together)

Skeletal remains can be seperated from natural processes such as weather and animals

How does Geographic location affect decomposiosition

• Temperature and humidity

• Hot/humid - increase

• Cold - decrease

How does Time of year affect decomposiosition

• summer vs winter

• urban (faster) vs rural (slower)

How does Exposure to sunlight affect decomposiosition

• Sun rays promote decay

• Sun + wind = mummify

• Body in fuld is avoided by invertebrates 

• Desiccation and UV light kill eggs

How does Wrapping and Confinement affect decomposiosition

slows

Wrappings make transport esier (tarps, carpets, shower curtains, suitcases, bins)

Insects and still permeate (some) wrappings - car boots

How does Hanging above ground affect decomposiosition

slows

No moist, dark, under-surfae for flies to lays eggs

Increased air circulation around body promotes drying out

Maggots fall off washed off by rain

How does underground Burials affect decomposiosition

slows

Soil type and chemistry

Heavy clay has lower oxygen which reduces microbial activity (slows)Burials - underground (slows)

Acidic soil reduces microbial activity (slows) but low pH dissolves tissues & bone (increases)

High calcium reduces chemical dissoution of bones but microbial decomposition continues

Depends on time of year, exposure to sun, rainfall, drainage, height of water table

Reduced blowfly, but other invertebrates will colonise

How does underwater burials affect decomposiosition

slows

Lower temperature and reduced oxygen

Decay occurs more slowly in salt water than fresh water (fewer micro-organisms)

Bodies on surface of water will decay faster than those on floor (access of insect)

Under-studied area of forensic science

How do Wounds affect decomposiosition

increases

Rapid discovery and exploitation by insects (increases)

Severe blood loss decreases the rate of decay (slows)

How does Burning affect decomposiosition

Intentional detection avoidance behaviour

Extreme high temperature necessary to completely destroy body

Extremities most affected

High fat content (increases)

Flammable clothing (increases)

Sterilised and dry skin (slows) but causes cracks to deeper tissue (increases)

How does Chemical treatment affect decomposiosition

slows

Acid can be used to destroy ecidence

Acid can also be used to preserve the body (quicklime)

How does Embalming affect decomposiosition

slows

Chemicals delay or prevent decompostition

Compromises evidence

Ways to determin PMI

Vitreous humor (fluid in the eyes)

Bone structure

Bone autofluorescence (UV light)

Chemical analyses - luminol

Radiocarbon dating

Determine of provenance

stable isotopes

Human travel, trafficking

Use of isotopes that don’t decay (carbon-12, carbon-15

Ratios can indicates diet, origin, movement

Strontium ratios (84Sr, 86Sr, 87Sr & 88Sr) vary geographically

Signature to area

Enter via diet and remain unchanged (tooth enamel) cf. strontium in metabolically active bones (where they spent the last few

Differences between various bones informative based on rate of remodelling