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

5
(No Transcript)
6
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

9
(No Transcript)
10
One day old dead pig showing signs of skin
changes and bloating.
11
(No Transcript)
12
(No Transcript)
13
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

14
(No Transcript)
15
One week old pig-larva develop migrate from
body to pupate
16
(No Transcript)
17
(No Transcript)
18
(No Transcript)
19
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

20
(No Transcript)
21
(No Transcript)
22
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)

23
(No Transcript)
24
(No Transcript)
25
(No Transcript)
26
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

30
(No Transcript)
31
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)

34
(No Transcript)
35
(No Transcript)
36

• 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

37
First instar
Third Instar
Second instar
38
(No Transcript)
39

• Pupal Stages of House Fly

40
(No Transcript)
41
(No Transcript)
42
(No Transcript)
43
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

47
(No Transcript)
48
(No Transcript)
49
(No Transcript)
50
(No Transcript)
51
(No Transcript)
52
First instar
Third Instar
Second instar
53
Maggots can consume 60 per cent of a corpse
in less than a week. Video footage R.
MajorWindows Media (77kb)Quicktime (275kb)

54
(No Transcript)
55
(No Transcript)
56
Burying Beetles
57
Hister Beetle
58
(No Transcript)
59
Forensic Flies
60
(No Transcript)
61
(No Transcript)
62
(No Transcript)
63
(No Transcript)