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Determining the Time of Death (TOD)

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Taking temperature of the maggot mass can find it as high as 125 degrees F. Forensic Entomology Using developmental stages of insects to determine TOD Adult ... – PowerPoint PPT presentation

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Title: Determining the Time of Death (TOD)


1
Determining the Time of Death (TOD)
2
Maggots and Murder
3
Forensic Entomology
  • Using the developmental stages of insects to
    determine TOD

Larvae
Pupae
Eggs
Adult
Adult
4
Forensic Entomology
  • The study of insects in relation to a
    criminal investigation.
  • Insects arrive at a decomposing body in a
    particular order and then complete their life
    cycle based on the surrounding temperature.
  • By collecting and studying the types of
    insects found on a body, a forensic entomologist
    can predict the time of death.
  • When one biological clock stops,
    others begin.
  • --Neal Haskell, reknown forensic entomologist

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Determining the Time of Death (TOD)Using
Forensic Entomology
7
Stages of Decomposition
  • Initial Decay-Although body shortly after death
    appears fresh from outside-bacteria in bodys
    intestine before death begin to digest intestine
    itself.
  • Autolysis-bacteria exit intestine and digest
    internal organs. The body's own digestive enzymes
    spread throughout body
  • Enzymes inside cells-released when cell
    dies-break down cell and connections with other
    cells
  • Flies are immediately attracted to dead bodies
    Without normal defense of living animal-
    blowflies and house flies lay eggs around wounds
    and body openings
  • Eggs hatch and move into body within 24 hours.
    Life cycle of a fly from egg to maggot to
    fly-2-3e weeks

8
Stages of Decomposition
  • 2. Putrefaction-4-10 days after death
  • Putrefaction-destruction of soft tissues by of
    micro-organisms-results in catabolism of tissue
    into gases and liquids
  • First visible sign-formation of sulfhaemoglobin
    in settled blood.
  • Releasing fluids into body cavities-anaerobic
    respiration - produce hydrogen sulphide, methane,
    cadaverine, putrescine, butyric and propionic
    fatty acids
  • Distention of gut-Gas build up from multiplying
    bacteria-internal pressure-inflates body and
    forces fluids from cells and blood vessels into
    body cavity
  • Rate of decay increases-blowflies, flesh flies,
    beetles and mites
  • Late-arriving insects-predators-feed on maggots
    and flesh -Maggot masses

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One day old dead pig showing signs of skin
changes and bloating.
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Stages of Decomposition
  • 3. Black Putrefaction-11-20 days after death
  • Bloated body collapses-creamy flesh-exposed parts
    are black in color and very strong smell of
    decay.
  • Body fluids drain from body and seep into soil
  • Insects consume most of the flesh and body
    temperature increases with activity.
  • Bacterial decay important-bacteria consume body
    if insects are excluded
  • Several generations of maggots-migrate from body
    and bury in soil to pupate
  • Predatory maggots are much more abundant
  • Pioneer flies cease to be attracted to corpse.
  • Predatory beetles lay their eggs in the corpse
    and their larvae then hatch out and feed on flesh

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One week old pig-larva develop migrate from
body to pupate
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Butyric Fermentation
  • 20-50 days after death
  • Dessication of corpse-remaining flesh is removed
    and butyric acid released
  • The surface of body in contact with ground
    becomes covered with mold as body ferments.
  • Beetle larva and adults feed on skin and
    ligaments.
  • Predators and parasitic wasps and beetles

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Dry Decay
  • 50-365 days after death
  • Body is dry and decays slowly-Eventually leaving
    only skeleton
  • Diagenesis-process that changes skeletons
    proportions of organic (collagen) and inorganic
    components (hydroxyapatite, calcium, magnesium)

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PMI--Postmortem Interval
  • PMI-amount of time b/w TOD and bodys
    discovery
  • Estimation of PMI- set minimal and maximal PMI
  • Minimal PMI -determined by estimating age of
    developing immature insects collected when corpse
    is discovered
  • Maximum PMI-determined from species of
    insects present and weather conditions needed for
    the activity of these species

27
Temperature
  • Ambient heat plays a role during egg and
    early larval development but after that its
    effect decreases rapidly. Maggot masses generate
    their own heat.

Taking temperature of the maggot mass can find it
as high as 125 degrees F.
28
Forensic Entomology
  • Using developmental stages of insects to
    determine TOD

Larvae
Pupae
Eggs
Adult
Adult
29
Forensic Entomology
  • The study of insects in relation to a criminal
    investigation
  • Insects arrive at decomposing body in a sequence
    and complete their life cycle based on
    surrounding temperature
  • Forensic entomologist can predict the time of
    death

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Metamorphosis
  • Complete metamorphosis (holometabolous)
    -development from egg to larva to pupa to adult
  • The white crust in the picture are the fly
    eggs.

32
Larva
  • Larva hatch from the eggs and increase in
    size by growth steps called instars.
  • Larva migrate from corpse and develop into
    an inactive pupal stage
  • During this time, the adult insect develops
    internally.

Two larval instars.
33
The Blowfly
  • Acts as both necrophages and as predator
  • One of the most common species on dead bodies
  • Often arrive within 10 minutes
  • Feed on blood and lays eggs in body cavities
  • If food source is exhausted- will prey on other
    species in same genus (Chrysomya)

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  • Maggots (fly larvae) are remarkable eating
    machines
  • Posterior spiracles
  • Spiracles are used for breathing-posterior
    spiracles-means that maggots can breath feed 24
    hrs a day

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First instar
Third Instar
Second instar
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  • Pupal Stages of House Fly

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Types of Insect Collections
  • Collection are done in three ways
  • Aerial
  • Hand
  • Live Sampling

44
Aerial Collection
  • Use a net in figure 8 motion over cadaver
  • Collect flies and put them in ethyl acetate
  • After a few seconds-put flies into 75 ethyl
    alcohol-label date, time, case , location,
    sample type and collector.

45
Live SamplingMaggot Motels
  • Collect 10 to 15 live maggots of varying sizes
    into a rearing chamber
  • Allow to develop into pupae and then into adults.

46
Hand Collection
  • Collect maggots with forceps
  • Put in boiling water to stretch them out and fix
    them
  • Put maggots into ethanol with a label containing
    date, time, case , location and collector

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First instar
Third Instar
Second instar
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Maggots can consume 60 per cent of a corpse
in less than a week. Video footage R.
MajorWindows Media (77kb)Quicktime (275kb)

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Burying Beetles
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Hister Beetle
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Forensic Flies
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