Time since death/PMI

1. Determination of time since death
ATULABHISHEK
M.Sc forensic science
GALGOTIAS UNIVERSITY, UP

2. Post-mortem Changes
The changes which occur after death that are helpful in estimation of the approximate time
of death can be classified into :
Immediate changes (Few minutes after death to maximum 30 minutes)
a) Insensibility and loss of voluntary power
b) Cessation of respiration
c) Cessation of circulation
Early changes (1-36 hours.)Early changes (1-36 hours.)
a) Changes in the skin
b) Changes in the eye
c) Cooling of the body (Algor mortis)
d) Postmortem lividity (Livor mortis)
e) Changes in the muscles (Rigor mortis, RM)
Late changes (>36 hours)
a) Decomposition (combination of autolysis and putrefaction)
b) Modifications of putrefaction (adipocere, mummification).

3. Change in skinChange in skinChange in skinChange in skin
Skin becomes ashy-white, pale and loses elasticity,
within a few minutes of death.
Lips are dry, brownish and hard due to drying.Lips are dry, brownish and hard due to drying.

4. Changes in the EyeChanges in the EyeChanges in the EyeChanges in the Eye
Change in eye after death
Note :- pupil dilation occurs after death but, when rigor mortis formation occur pupil become
contract.

5. Tache noire - If the eyelids remain open after death, desiccation of
sclera occurs giving rise to somewhat triangular shaped discolored
areas [simplyTache noire (black spots)].These are yellowish in color
in the beginning, but as dust settles in, they become dark red or later
even black.
Tache noire

6. Loss of intraocular tension-
Intraocular pressure (IOP) falls rapidly after death. It becomes
zero in 4–8 h from 10–20mmHg (Average–15mm )during
life. Due to this,The eyeballs look sunken in the orbit.
value IOP
15 At death
12 After 1 hr
10 After 2hr
8.5 After 3hr
7.5 After 4hr
5 After 8hr

7. Vitreous humour
IOP

8. Rising potassium level in vitreous humour:
After death, the cells around the vitreous chamber breakdown
and release their fluid in the vitreous, due to this the
concentration of ions slowly increases.
Increasing concentration of ions in vitreous chamber provide a
remarkable data of time since death and medical history.
If a body finding in underground water, in this case theIf a body finding in underground water, in this case the
environmental conditions make difficulties to determine the time
of death, but examination of potassium level give estimate time
since death.

9. Time of DeathTime of DeathTime of DeathTime of Death———— AlgorAlgorAlgorAlgor MortisMortisMortisMortis
cooling of the body
Body heat falls after death
Average rate of fall -
(a) during summers -0.75°F/h (b) during winters -1.5°F/h.
Heat loss is affected by the ambient temperature( environmentalHeat loss is affected by the ambient temperature( environmental
temperature)
Corpse temperature is measured by a thermometer inserted into
the liver or rectum.
Time of death is expressed as a range of time

10. Temperature is measured by using a chemical thermometer graduated
from 1 to 50 degrees centigrade, inserted 10 cm into the rectum.
When there is history of suspected sexual assault, then the temperature
is measured from the under surface of the liver by making a slit opening
on the upper part of right side of the abdomen (sub-hepatic
temperature).
Time since death = Normal body temp – Rectal temp/subhepatic temp
Rate of fall ofTemp/hour
Example:
= 37 ˚C(Normal temp) – 35.5˚C(measured)
1.5˚C(constant)
=1 Hour.

11. Factors affecting the rate of cooling:Factors affecting the rate of cooling:Factors affecting the rate of cooling:Factors affecting the rate of cooling:----
I. Age: The bodies of old people and children cool faster than adult bodies.
II. Condition of Body: Fat and large bodies cool slowly due to fat which is a
bad conductor of heat, ; hence females and obese bodies cool slowly.
III. Manner of Death: The bodies of persons who were suffering from chronic
or wasting diseases cool faster than persons dying of violent reasons.
IV. Atmosphere: If a body is in open air, it cools faster. It also cools faster
when in water.when in water.
V. Clothing: Coverings on or around the body; clothing prevents heat loss
from the body.
Postmortem caloricity:
It is a condition where there is rise of body temperature after death instead
of cooling of the body.
postmortem glycogenolysis, can produce up to about 140 calories that can
raise the body temperature about 2° C

12. Time of DeathTime of DeathTime of DeathTime of Death————Rigor MortisRigor MortisRigor MortisRigor Mortis
The stiffening of muscle after Death
Without oxygen in the blood—
Calcium accumulates in the muscles
Muscles stiffenMuscles stiffen
Starts in the eyelids and expands throughout and lastly the
lower limbs.
After about 15 hours—
Muscle fibers begin to dissolve
Softening begins

13. Live muscle fibers slide
back and forth
After death, muscle fibers
become locked in a flexed
position

14. Time of appearance: (Rule of twelve)
• Starts in 3 to 6 hours
• Takes 12 hours to complete
• Stays for another 12 hours
• Passes off in the next 12 hours.
Observation Approx. Time Scale
The body is at its most rigid state Just over 2 hours
No visible signs of rigor
Less than 2 hours
or more than 48 hours ago
Rigor mortis completed 12 hours
Stiffness generally disappears After 36 hours

15. Time of DeathTime of DeathTime of DeathTime of Death————Livor MortisLivor MortisLivor MortisLivor Mortis
Lividity begins about 2 hours after death.
Discoloration becomes permanent after 8 hours
Ambient temperature affects the speed of decomposition.
Cooler temp – occurs slower
Warmer temp – occurs fasterWarmer temp – occurs faster
Lividity can determine the position of the body during the first eight
hours.
The normal colour of livor mortis changes from red to purple as
oxygen gradually dissociates from the hemoglobin of red blood cells.
This produces deoxyhemoglobin that is purple in colour and therefore
postmortem lividity normally looks purplish.

16. Post-mortem lividity

17. Formation of lividity over dependent part of body

18. Time of DeathTime of DeathTime of DeathTime of Death
————Stages of DecompositionStages of DecompositionStages of DecompositionStages of Decomposition
A. Within 2 days. : Initial Decay (Fresh)
Cell autolysis begins.
Green and purplish staining occurs from blood
decomposition.
Skin takes on a marbled appearance.Skin takes on a marbled appearance.
Face becomes discolored.
B. After 4 days : Putrefaction (Bloating)
Skin blisters.
Abdomen swells with carbon dioxide (released by
bacteria living in the intestines).
Lecithinase is major bacterial enzyme responsible
for putrefaction.

19. C. Within 6-10 days : Decay stage - Black
Putrefaction (Butyric Fermentation)
Corpse continues to bloat with CO2 as
bacteria continue to feed on tissues
Eventually, gas causes chest and
abdominal cavities to burst and collapse.
Fluids begin to leak from body openings as
cell membranes rupture
Eyeballs and other tissues liquify
Skin Sloughs off
Very strong odor

20. D. Within 10-25 days : Post decay Stage- Butyric
Fermentation
Corpse is beginning to dry out
Most of flesh is gone
E. >25-50 days : Dry Decay (Skeletonization)
Corpse is almost dry
Further decay is slow due to lack of moistureFurther decay is slow due to lack of moisture

21. Time of DeathTime of DeathTime of DeathTime of Death————InsectsInsectsInsectsInsects
Forensic entomologist
Collects insect evidence from on, above, and below the body
Records environmental conditions
Within hours of a death, certain insects arrive to lay their eggs onWithin hours of a death, certain insects arrive to lay their eggs on
the warm body—blowflies
As the corpse decomposes, other kinds of insects arrive

22. Time of DeathTime of Death
——Blowfly Life CycleBlowfly Life Cycle
1. <8 hours after death—blowfly eggs can be found in the moist,
warm areas of a corpse
2. Within 20 hours—1st of their 3 larva stages
3. 4th or 5th day—3rd of their 3 larva stages3. 4 or 5 day—3 of their 3 larva stages
4. 8 to 12 days—larvae migrates to a dry place
5. 18 to 24 days— Early pupa; immobile; changes from light brown
to dark brown
6. By the 21st-24th day the pupa cases will split open and adult
blowflies will emerge.

23. pupa
Adult
eggs
3rd instar
larva
2nd instar
larva
1st instar
larva
Life cycle of blow flyLife cycle of blow fly

24. Stage When first appears Stage Duration Characteristics
Egg Soon after death 8 hours
Found in moist, warm
areas of body.
Mouth, ears, anus
Larva 1
(Instar 1) 1.8 days 20 hours
1 spiracle slit near anus
Thin body
Larva 2
(Instar 2) 2.5 days 15-20 hours
2 spiracle slits near anus
Starts feeding
Larva 3
(Instar 3) 4-5 days 36-56 hours
3 spiracle slits near anus
Fat body
Pre-pupa 8-12 days 86-180 hours
Larvae start to migrate
away from body
Early and late pupa
stages 18-24 days 6-12 days
Immobile, doesn’t feed
Changes to dark brown
Adult 21-24 days Several weeks
Hatched from larvae
Immobile for first few
hours

25. PMI Calculation ExamplePMI Calculation ExamplePMI Calculation ExamplePMI Calculation Example
Larva
1st
Larva
2nd
Larva
3rd Pre-
Total
time
Body is found with Lucilia sericata larvae, prepupae, and pupae (in soil next
to body). Temps at site had averaged 16°C. Pupae brought into the lab &
held at that temp. began to enclose after 112 hours.
Development rate of sheep blowflies, Lucilia sericata, (in hours) at three different
temperatures
Temp(°C) Egg
1st
Instar
2nd
Instar
3rd
Instar
Pre-
pupa Pupa
time
(days)
16 41 53 42 98 148 393 32
21 21 31 26 50 118 240 20
27 18 20 12 40 90 168 14
PMI = (41 + 53 + 42 + 98 + 148 + 393 – 112)/24 = 26.5 days

26. Life cycle of house flyLife cycle of house fly

27. Diagrammatical representation of Estimation of time
since death

28. Time of DeathTime of DeathTime of DeathTime of Death
————Stomach and Intestinal ContentsStomach and Intestinal ContentsStomach and Intestinal ContentsStomach and Intestinal Contents
State of Contents Timing of Death
Undigested food present in the
stomach
Zero to two hours after the last
meal
Stomach is empty, but food
found in small intestine
Death occurred at least four to
six hours after a meal
Small intestine is empty; waste
found in large intestine
Death occurred 12 or more
hours after a meal

29. ReferencesReferencesReferencesReferences
BISWAS, G. (2015). REVIEW OF FORENSIC MEDICINE AND
TOXICOLOGY:Including clinical & pathological aspects. Jaypee
Brothers Medical Publisher.
Aggrawal,A., Dr. (2016). Forensic Medicine andToxicology for
MBBS.AVICHAL PUBLISHING COMPANY (APC).MBBS.AVICHAL PUBLISHING COMPANY (APC).
Reddy, K. N., & Murty, O. (2015). The Essentials Of Forensic
Medicine AndToxicology. Jaypee Brothers Publisher.

30. THANK YOU !!!!THANK YOU !!!!