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Forensic Evidence The time of death is a critical piece of information for investigators attempting to understand the cause of suspicious deaths. Factors to be investigated. 1. Temperature: The temperature of a body can be used to estimate time of death during the first 24 hours .

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slide1

Forensic Evidence

The time of death is a critical piece of information for investigators attempting to understand the cause of suspicious deaths.

slide2

Factors to be investigated.

  • 1. Temperature:
  • The temperature of a body can be used to estimate time of death during the first 24 hours.
  • Core body temperatures fall gradually with time since death, and depends on body mass, fat distribution and ambient temperatures at the site of death.
  • The body needs to be discovered before it comes into equilibrium with the ambient temperature at the site of death.
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2. Rigor mortis The presence of rigor mortis also assists forensic scientists in determining the time of death. The body muscles will normally be in a relaxed state for the first three hours after death, stiffening between 3 and 36 hours, and then becoming relaxed again.There are considerable uncertainties in time estimates based on this factor. The time of death is very dependent on the amount of work (movement, struggle) the muscles had been involved with before death.

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3. Insects

The presence of insects in and on a corpse is a critical clue towards estimating the time of death for bodies dead for longer periods of time.

This leads us into a branch of Forensic Entomology.

Our program includes examples of Laboratory work

and Field Work

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Forensic Entomology

Entomology is a branch of zoology that studies insects. Entomologists are scientists that specialized in all the details about insects, their life histories, morphology, embryology, development, taxonomic classification. Forensic Entomologists use knowledge about insects to determine the time of death of a body.

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Insect Taxonomy

Taxonomy involves the identification, naming, and classification of plant and animal species. Botanist Carolus Linnaeus developed a two part Latin name for each species. Common names vary, the Latin binomial genus and species names do not. Example: Culexpipiens= common mosquito.

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Forensic Entomologists useinsect reference

  • collections and insect morphology to identify adult
  • insects.
  • Collecting and growing larvae to adulthood aids in
  • verifying identification of the adult.
  • Careful documentation of the evidence is very
  • important to the forensic scientist.
  • The larval component of the insects life cycle can be
  • used to determine the time of death of the body.
fly reference collection from private collections universities or museums
Fly reference collection from private collections, universities or museums

Adult fly morphology is used to identify the specimen.

fly reference collection
Fly reference collection

Adult flies in reference collections aid in positive identification.

insect morphology
Insect Morphology

Insect identification by taxonomic keys requires knowledge of insect morphology. (the insect body form and structure)

fly morphology
Fly morphology

Flies have no nose, their antennae are their smell sense organs which collect chemical molecules in the air that will direct the fly to food. Its tongue, labella “lick up” food molecules.

fly dichotomous taxonomic key
Fly Dichotomous Taxonomic Key

Understanding fly morphology (what they look like) allows unknown specimens to be identified by taxonomic keys.

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Forensic Entomology : Adult fly and beetle insect taxonomy.

Insects belong to the

Kingdom: Animalia

Phylum: Arthropoda (jointed legged animals)

Class: Insecta

Order: Diptera (Flies) Order: Coleoptera (Beetles)

Family: Muscidae Family: Carabidae

Genus: Musa Genus: Nicrophorus

Species: domestica Species: marginatus

Scientific Name: Scientific name:

Musa domesticaNicrophorusmarginatus

Common Name: Common name:

Housefly Carrion beetle

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Corpse Fauna: Bacteria

  • When a body dies bacteria decompose it by breaking down complex molecules through respiration or fermentation (depending on whether they are aerobic or anaerobic bacteria).
  • The odors generated are detected by insect who are then attracted to the body. Insect physiology tell us that they have an acute sense of smell.
  • Sense organs on the insect’s antennae collect the chemical signals. The first insects to arrive are the adult flies then later the beetles.
  • The Forensic Entomologist must use his/her knowledge about insect to analyze the crime scene.
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Corpse Fauna

  • The larvae of flies (maggots) are the most obvious and abundant fauna present on corpses in the early stages of decomposition.
  • House flies (Family Muscidea) and blowflies (Family Calliphoridae) are the first to arrive at the body. Flies in both of these families lay eggs which develop and hatch out as larvae.
  • The larvae feed on the fluids that seep from the body. Later they enter the body and feed on the all decaying tissue. Maggots can eat 60% of a corpse in less than one week.
  • Fleshflies (Family Sarcophagidea) arrive and give birth to larval maggots. They feed on body tissue.
slide17

Blow Flies

  • The blow fly Luciliasericata is well known by the entomologists.
  • They are about the size of a house fly and are metallic blue or green in color.
  • Flies rapidly discover a corpse and are the first inhabitance of the body.
  • Forensic Entomologists use information about the flies life cycle to help determine the time of death
slide18

Flies and beetles under go a Life Cycle called

  • Complete Metamorphosis. They change from a
  • sexually immature form into an adult.
  • The cycle starts with an egg
  • That changes into a larval form that grows
  • (eats a lot) ,
  • That changes into a pupa
  • (it stops feeding- creates a protective coat and
  • Then undergoes a final transformation into the adult.
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In lab, growth of different fly species from eggs to

  • adult forms is well documented.
  • Very Important:
  • When were the eggs were deposited on the body
  • and the number of hours between each stage is a
  • key to when the body died.
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Beetles

  • As the body continues to decay beetles arrive at the corpse. Beetles have chewing mouthparts and can eat tougher food.
  • The first to arrive are predatory adult beetles like the rove beetle (Family Staphylinidae) and the hister beetle (Family Histeridae). They eat fly larvae. They lay their own eggs which hatch as larvae with their parents jaws. They can eat fly larvae
  • Late arriving species like the hide beetle (Family Dermestidae) feed on the skin, ligaments and tendons of the body. The carrion beetle (Family Silphidae) are predators on larvae and will eat decaying flesh.
entomology collection beetles
Entomology Collection: Beetles

Identifying actual adult beetles from reference collections of private collectors and museums.

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Todays Assignment is Entomological Evidence Collection and Determining the Time of Death.

  • Your 5 member team need assignments.
  • Each investigator must carefully collect and
  • document entomological data.
  • Your team needs to select a Group Oversite Supervisor.
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Your forensic team will complete the following tasks:

Task Assignments for Investigators (A-E):

*Task A: Oversite Supervisor. Facilitates the creation of Investigator teams and task assignments.

(1 Investigator) Verify accuracy of all evidence and data collection, each team investigator

must sign their complete name on the Report of Examination of Entomology Evidence.

* Task B: Crime Scene

(1 Investigator) Death Scene Documentation. Data: photographs, observations, notes, etc.

*Task C: Laboratory Data Collection

(1 Investigator) Create Sketches , Life Cycle Reference Collection.

(1 Investigator) Create Sketches , Life Cycle Reference Collection.

(1 Investigator) Collect metric measurements of specimens. Larval dimension specialist.

*Task D: Field Work

(1 Investigator) Collect samples from the cadaver. Larval Maggot Collection.

*Task E: Laboratory Work

(1 Investigator) , Create sample bottles, Larval Maggot Preservation.

(1 Investigator) Create a Maggot Motel. Larval Maggot Rearing. Verify adult insect species via

larva collected at the crime scene.

(1-2 Investigators) Clean-up Technicians, Observe-note start up location of all material,

monitor time remaining, inform colleagues, return all materials to their start up locations

*Task F: Data Analysis

Oversite Supervisor: CONSULT with your Group Team. Discuss-Evaluate all Entomological

Evidence. Will it “hold up” in court?Determine the Time of Death.

(Estimated Date/Time in Hours.)

Staple together your team documents and submit your report to your Class Instructor.