Determining Time Since Death

1
Determining Time Since Death

• Postmortem Interval

2
The Postmortem Clock

• Following death, numerous changes occur that
  ultimately lead to the dissolution of all soft
  tissues. The importance of these changes to the
  forensic pathologist is that they provide a
  sequence of events that allow an estimate of time
  since death. This determination is based on the
  principle of sequential changes called the
  postmortem clock.

3
The Postmortem Clock

• The evaluation may include the following
  phenomena
• Changes evident upon external examination of the
  body, such as temperature, livor, rigor, and
  decomposition
• Chemical changes in body fluids or tissues
• Physiological changes with progression rates,
  such as digestion
• Survival after injuries, based on the nature,
  severity, and other factors such as blood loss

4
The Postmortem Clock

• Because of the variation inherent in each of
  these processes, an initial time range of death
  is established and modified as more information
  becomes available
• This initial time range is the interval prior to
  which it may be asserted with some evidence that
  the victim was alive, based on witness sightings,
  signed documents, or other established events.
• This initial time range is then modified by
  various methods of evaluating postmortem changes

5
Algor Mortis

• Postmortem cooling, or algor mortis, occurs at a
  rate of about 2 - 2.5 per hour at first
• Then it slows down to about 1.5 during the first
  12 hours, and decreases further after that
• Many factors, such as ambient temperature,
  clothing, and air currents, can affect postmortem
  cooling and, although it is still relied upon, it
  is known that the accuracy of this method is low

6
Eyes

• The eyes are also an indicator of postmortem
  changes
• Because the circulation of blood ceases, blood
  settles in the innermost corners of the eyes
• If the eyes remain open, a thin film forms on the
  surface within minutes and clouds over in two to
  three hours if they are closed, it may take
  longer for this film (an hour or more) and
  cloudiness (24 hours) to develop

7
Points Already Discussed

• Livor Mortis
• Rigor Mortis
• Stomach Contents
• Small meals 1.5 2 hours
• Medium meals 3 or 4 hours
• Large meals 4 6 hours
• Meals eaten quickly will take longer
• Alcoholic beverages delay stomachs evacuation

8
Decomposition of the Body

• Begins almost immediately after death and
  consists of two parallel processes
• Autolysis the disintegration of the body by
  enzymes released by dying cells
• Putrefaction the disintegration of the body by
  the action of bacteria and microorganisms

9
Four Main Stages of Decomposition

• Fresh
• Bloated as the gaseous by-products of bacterial
  action build up in the body cavity
• Decay ranging from wet to mushy to liquid
• Dry
• These changes depend in large part on the
  environmental factors surrounding the decedent,
  such as geographical location, seasonality,
  clothing, sun exposure, and animals and insects
  in the area. Insect activity, when present,
  greatly assists the decomposition process.