chapter 5: PMI

postmortem interval (PMI)

• the length of time since death

• one of the statistics used to examine missing persons files in search of a likely match

methods to estimate PMI

1. livor mortis

2. algor mortis

3. changes in vitreous humor (changes in the fluid in the eye)

taphonomy

the study of how organisms decay and eventually become fossils; included everything that affects the body and skeleton as it decomposes and breaks down

three key forensic fields that helps determine PMI

• forensic pathology/anthropology

• forensic entomology

• forensic botany

forensic taphonomists

• studies the stages through which human body passes from being fresh to being freshly skeletonized

• also studies the schedule by which animals eat, disarticulate, and modify biological remains

forensic entomology

the study of insect life cycle and succession on cadavers for the purpose of determining PMI

forensic botany

use plant growth as a method of estimating PMI

decomposition

the process by which soft tissues breaks down and a body eventually becomes skeletonized

skeletonization

the final stage of decomposition, during which the last remnants of tissue have broken down and the skeleton becomes visible

initial process of decompositiol

1. autolysis

2. putrefaction

autolysis “self-digestion”

• first stage of decomposition

• refers to the degeneration of body tissues by the digestive fluids normally residing in the intestinal act

algor mortis

• refers to body temperature cooling after death

• dependent on ambient conditions

livor mortis

• refers to pooling of blood in the lowest parts of the body and to discolouration

• occurs within 2 to 4 hours and reaches a max between 8 to 12 hours after death

rigor mortis

• the stiffening of muscles from chemical binding of muscle fibres

• eases as the fibre break down due to enzyme action

• reaches a maximum within 6 to 24 hours after death

• dissipates between 12 and 36 hours after death

• accelerated by heat and decelerated by cold

putrefaction

• the breakdown of the body by bacteria which are naturally present, it follows rigor mortis

• fed by the release of nutrients through autolysis

bloating

the result of hydrogen sulphide gas being release from bacterias

marbling

bacteria also invade blood vessels causing blackening effect

adipocere

• a waxy, soap-like substance formed by the accumulation of hydrated body fats

most important factors that speeds decomposition

1. temperature: affects plant and animal activity (warm areas with greater insect activity)

2. humidity: slows the drying of soft tissue, decomposition is faster in humid climates while arid climates cause rapid dehydration leading to natural mummification

3. accessibility:

burried remains

• decomposition is slower

• less insect activity

• less chance of dispersal from scavengers

submergence

• submergence in water also slows the process down

• submerged bodies also show significant bloating from water uptake

scavenging

• human remains are often scavenged vy carnivores and occasionally rodents can cause disarticulation and scattering remains