Post-mortem interval

FIND THE TAPHONOMY BOOK

Notes

Decomposition (broad categories)

• Terrestrial

  • Fresh

  • Bloat

  • Active decay

  • Advanced decay

  • skeletal

• Aquatic

  • Fresh submerged

  • Floating bloated

  • Early floating decay

  • Advanced floating decay

  • Exposure of skeletal elements

  • sunken remains

  • skeletal

Time since death

PMI is the amount of time that has elapsed since the time of death

• integral to medico-legal investigation

• Narrows field of suspects

• Validates witness statements

• Limits number of suspects and assesses their alibis

• Missing persons

Defining death

• Medical and Legal criteria

  • Cardiopulmonary criteria

  • Neurological criteria

Death- the irreversible cessation of blood circulation → decomposition → Autolysis and Putrefaction

Putrefaction- liquidefication of tissues

Autolysis v Apoptosis

• Autolysis is the destruction of an organism’s cells by enzymes produced by the cells themselves

  • Autolysis is unintentional

  • Does not happen in healthy tissues

  • Is not a controlled process

  • Results in harmful effects on surrounding cells or tissues

• Apoptosis is a form of programmed cell death in which cells undergo an ordered sequence of events which lead to its death (A part of normal growth and development)

  • Is intentional

  • Occurs in healthy tissues all the time

  • Is a controlled process

  • Does not produce harmful substances which interfere surrounding cells or tissues

External factors

• Environment

  • Temperature

  • Moisture

  • Soils

  • Clothing

• Living impacts

  • Insects

  • Predators

PMI

Three stages

• Immediate, early and late → Up to 72 hours → Early PMI indicators (algor mortis [temperature], rigor mortis [stiffening], and livor mortis [color])

Algor Mortis

• Cooling of the body after death (avg. 1.5 degrees F per hour)

  • Temperature → Henssge’s Nomogram

    • Need to know:

      • Rectal temperature

      • Ambient temperature

      • Body weight

    • Most precise in the first 10 hours post mortem

      • Steps:

        • Take the rectal and ambient temps, draw a line between the two

        • Find the cross hair and take a line out

        • Find the weight and time that corresponds

        • Add varriation based on clothing

• Add henssge’s nomogram photo

  •  Limitations:

    • Changes in ambient/ environmental temperature

    • BMI

    • Type of clothing

Rigor mortis

• Commences about 2 hours after death and completes about 6 hours

• Caused by the depletion of ATP from the muscles

• Procedes in sequence

  • Smaller muscles first (mouth and eyes)

  • Progressing downward to upper limbs and hands

  • and then Larger muscles

• Nysten’s law

• Dissolution of stiffness commences around 24 hours, in the opposite order

• Rigor mortis absent after 36 hours

• Dependent on:

  • Temperature

    • Cold delays rigor mortis

  • Cause of death

    • Carbon monoxide for example

  • Sex

  • Age

Livor mortis

• Purplish-blue/ waxy discoloration of the skin

• Spots of discoloration within half an hour

• Coalesce within 6-12 hours

• Maximum intensity of color by 12 hours

  • Influences

    • Blood loss

    • Submersion

Late PMI

Decomposition of protiens, breakdown of tissues, and liquefication of organs

• 48 to 72 hours

  • Greenish color

  • Marbling of skin

• 2 to 6 days

  • Bloating

  • Hydrogen sulphide, methane

• Influences

  • Temperature

  • Summer v. Winter

  • Moisture

  • Biotic factors influencing pattern and rate of decomposition

    • Forensic entomology

    • insects typically attracted the chemical outputs of decomposition

• From 5-11 days

  • Body deflates

  • Gasses released

  • Liquids drain from body via orifices

• From 28 days onwards usually …

  • Degredation of ADIPOSE tissue

    • mainly lipids (triglycerides)

  • Adipocere formation

    • Warm, wet, slightly alkaline environments

    • patches or whole body

    • highly variable

  • Advanced decomposition phase

    • Loss of soft tissue/ leathery skin

    • Exposure of some skeletal material

    • Desiccation and mumification (depending on the environment)

    • Skeletonization

Poster assignment

• Design a taphonomy facility in kent

  • Human or animal and why?

  • Why do we need them

    • What aspect of decomp with it focus on

    • Are you interested in an environment

  • Bear in mind forensic realism

    • environment

    • security

    • ethics

    • mindful of costs involved

INCLUDE REFERENCES