Post Mortem Interval
• Post-mortem interval (PMI) or Time since
death(TSD) is the time period between death
and examination of the body.
• Important because:
CREDIBILITY OF SUSPECT: one can check
the credibility of suspects statement.
MOMENT OF CRIME: it informs when
crime was committed.
VITAL LEADS TO THE PATIENTS:
it gives police a vital leads and starting points for
if a suspect was not in the city during the time of
death, he can excluded.
CHECKS ALIBI: it can confirm or disprove an
• Estimation of post-mortem interval or time since death is an
important goal in medico legal investigation.
• Determination of the time of death is important in both
criminal and civil cases.
- in criminal cases it is important to catch the killer.
-in civil cases it may become important in deciding
i)who inherit the property.
ii)whether at the time of death insurance policy was in
• It is also of crucial importance for forensic investigators,
especially when they are gathering evidence that can
support or deny the stated actions of suspects in a crime.
• After death, many changes begin to take place
in the body due to physical ,metabolic,
autolysis, physiochemical and biochemical
• These changes progress in an orderly manner
until the body disintegrates.
• The measurement of these changes along with
time is used for estimating time since death.
DETERMINATION OF PMI
• What Time Did the Person Die?
– Best estimate; offered with a reasonable degree of
medical and scientific certainty.
– Impossible to be 100% accurate.
– UNLESS a witness (who doesn’t lie) is present at
the time of death, it generally is an estimate of
time (2-4 hour window is the usual).
•Methods for estimating the post-mortem interval date
back to the ancient Greeks and Egyptians during the third
and forth centuries . They understood that dead bodies
cooled and became stiff over a period of time after death.
• Warm and not stiff: Dead not more than a couple of
• Warm and stiff: Dead between a couple of hours and a
• Cold and stiff: Dead between a half day and two days
• Cold and not stiff: Dead more than two days
Indications of Death
• Indications of death:
– Loss of all reflexes
– No reaction to painful stimuli
– Muscular flaccidity
– Cessation of heart beat and respiratory movement
– Eye signs:
• Loss of corneal and light reflexes
• Mid-dilated position of the pupils
• Irregular size and shape of the pupils
• Eyelids usually closed incompletely
• Tache noire: where the sclera remains exposed, two triangles of
discoloration appear at each side of the cornea, either brown or
• Bichat, concept of tripod of life,
A)Insensibility and lose of movement-cessation
of CNS function.
B)Cessation of respiration
C)Cessation of circulation
Other changes-stature, immediately after death
body lengthen by 2-3cm.
A)Change in skin- becomes ashy-white,pale and
loses elasticity within a few minutes of death.
B)Changes in the eye-
a)Dilate and fixed pupils.
-Normal size during life-1-8mm.
-pupil reacts to atropine and pilocarpine
for about 2hrs after death(till molecular death)
b) Absence of corneal and light
c)Opacity of the cornea-
-Cornea becomes opaque about
6hrs after death(time period up
to which cornea can be
harvested for transplantation)
-Tache noires(black spot)-if the
eyelids remain open after
death, desiccation of sclera
occures giving rise to
triangular shaped discoloured
area, initialy yellow in colour
but as dust settles in becomes
dark red or black.
d)Flaccidity of the eyeball-
-Eyes look sunken and are softer after death due fall
of intraoccular prassure(IOP)
-Normal IOP during life is between 10-20 mm Hg
1 hour after death-12 mmHg
2hrs after death-10mmHg
3 hrs after death-8.5mmHg
8hrs after death-5mmHg
-Absence of intraocular fluid suggests more than 4
-IOP gives a rough of PMI
Segmentation of the retinal blood columns
(Kevorkian sign) accrues immediately after
Colour of retina-become pale after death, and
become more and more pale as time of death
Disk outline become hazy after few hrs.
• Following death many physiochemical
changes occur to the body
Algor Mortis: Body temperature after Death
Livor Mortis: Discoloration after Death
Rigor Mortis: Stiffness after Death
• Putrefaction and Autolysis
• Algor Mortis (Body Cooling,chill of deth)
– Cooling of the body occurs after death since all metabolism comes
to a stop.
– During life heat is constantly transferred from one body part to
another by conduction as well as convection(through blood flow).
– -There is some production of heat during initial period after
somatic death due to ATP molecule breakdown(up to 2hrs) and
anaerobic glycolysis(much longer)
– Rectal temperature fall or not at all during first 2 hrs.
– Cooling occurs from surface to the surroundings.
– -Core temperature is the temperature of vicera,it is slightly
increased as compred to the body surface temperature.
– Core temperature is a better guide to TSD than surface
– Body cooling is inaccurate in obtaining time of death.
• Site for core body temperature-
Rectal temperature –best method- Insert a
thermometer 8-10 cm in rectum and left for 2-3min.
auditory meatus , nostrils or under the liver, brain.
Things to be recorded-
i)Temp of body ii)Temp of environment iii)Time of
recording iv) at least 5 reading at the interval of half
hours to calculate the rate of fall.
Calculation of time since death
– At 70°F – 75°F, the body cools 2.5°F to 2.0°F for first hour,
– then 1.5°F to 2.0°F for next twelve hours,
– then 1.0°F for next 12 hours.
Time since death = 98.6°F – Rectal Temp (°F)/ 1.5 or(37.2-rectal temp )/0.6
• The rectum should be checked before insertion of the thermometer
(May have been a sexual assault)
– Patient may not die immediately after assault.
• This may change time of death by several hours.
• Thumb rules
Time since death = 37°C – Rectal temperature (C) + 3
Factors affecting Rate of Cooling
• Body weight:
– Larger bw: slower cooling
– Smaller bw: faster cooling
– slower cooling rate.
• Surface area of the body:
– Larger surface area speeds up cooling rate.
– Children have an increased surface area which allows for
rapid heat loss.
• Clothing and emaciation
• Environmental Temperature:
– Higher humidity: rapid cooling rate
– Rapid air velocity: rapid cooling rate
– Rapid cooling rate:
– More rapid in flowing water than still water
• If there is a fulminating infection, e.g. septicemia,
the body temperature may continue to rise for some
hours after death.
Post mortem lividity(livor mortis)
• Livor mortis- Suggilation
,vabices, hypostasis, staining,
darkening of death.
• Purplish-blue discoloration due
to the settling of blood by
gravitational forces within
dilated, toneless capillaries of
• Livor mortis can be seen as
early as 30 minutes after death.
Since lividity results from the
heart stopping, it may begin
appearing antemortem in
decedents who die as a result of
cardiac failure. This stains the
Post mortem lividity commences
with in an hour after death.
Present as mottled patches in
dependent parts with in 1-3 hours
Patches gradually increase in size
and coalesce in about 2-6 hours .
Lividity is fully developed and
fixed i.e. becomes unchangeable
in about 6-8 hours.
Finally disappears when
putrefaction sets in >8hrs
Pressure of thumb- Blanches
(Not fix) TSD <8hours.
Pressure of thumb- Does not
blanches (Fix) TSD >6hours
• After death muscles are
initially flaccid and can be
• The flaccidity is followed
by increasing stiffness or
rigidity of the muscles.
• Joints are frozen.
• The rigidity will gradual
subside and the body will
be flaccid again.
– Chemical changes causes muscle mass to become rigid; looks like
body is frozen in place (fixed)
– Small muscles go into rigor first
– Rigor usually occurs from head to toe
Order of appearance and disappearance –
• Heart (left chamber in 1 hour)
• Eye lids ,Face muscles(2-3hrs)
• Neck and trunk (3-4hrs)
• Upper extemities (6hrs)
• lower extermities(9hrs)
• Small muscle of finger and toes( last to be affected 11-
• It passes off in same order of appearance
• It takes 12 hr to develop from head to foot , persists for
another 12 hr and takes 12 hr to pass off.
• In summer 18- 36 hr and In winter 24- 48 hr.
• This is dependent on environmental temperatures
• Fully flaccid body by 36 hours.
• Rigor is accelerated by
– Prior exercise
– Hot environmental temperatures
– Age (does not form well in children)
– Strychnine poisoning
• Rigor is inhibited by
– Cold environment
Factors affecting timing of RM
• Environmental temperature:
– Cold and wet onset slow, duration longer
– Hot and dry onset fast, duration shorter
• Muscular activity before death:
– Muscles healthy and robust, at rest before death slow onset, duration
– Muscles exhausted/ fatigued onset rapid, esp in those limbs being
used (eg in someone running at time of death, lower limbs develop RM
faster than upper limbs)
– Increase activity (convulsions, electrocution, lightning) rapid onset
& short duration
– Extremes of age rapid onset
• Cause of death:
– Asphyxia, pneumonia, nervous de’s with muscle
paralysis & dehydration slow onset
– Septicemia & poisoning rapid onset, may even be
absent, especially in limbs affected by septicemia
– Emaciated or died of wasting disease rapid onset,
RM: time estimation
Warm Flaccid Death < 3 hrs
Warm Stiff 3-8 hrs
Cold Stiff 8-36 hrs
Cold Flaccid Death > 36 hrs
• The disintegration of body tissues after death
• Tissue components leak and release hydrolytic
• Bacteria and other microorganisms thrive on the
organic material of the body
• Two parallel process of decomposition occur:
– Autolysis: Self-dissolution by body enzymes released
from disintegrating cells
– Putrefaction: Decomposition changes produced by
the action of bacteria and microorganisms
• The normal final sign of death.
• Starts immediately after death at the cellular level
• Becomes visible in 48-72 hrs.
• Its onset may be sped up or delayed by several
• The ambient temperature can speed up or slow down this
• A fever prior to death can speed up putrefaction
• One week in air equals two weeks in water and eight weeks in soil
• The 1st visible sign of putrefaction is green or greenish red
discoloration of the skin of the anterior abdominal wall
– Normally starts in the right iliac fossa.
• The Next phase:
– Gas formation
– Blisters containing red fluid appear on the skin,
mistaken as bleeding
• Humidity, temperature, bacterial activity body proteins break into
polypeptides & amino acids
• Brain & Epithelial tissues are the 1st to be affected by putrefaction
• Heart, Uterus & Prostate may survive for longer periods.
• Military Plaques: nodules in heart (epi/endocardial)
• Marbling: bacteria colonize venous system hemolysis stain.
The decomposition of a body can be divided into several stages,
even if the duration of each stage may vary a lot:
• 2 - 3 days: green staining begins on the right side of the abdomen.
– Body begins to swell.
• 3 - 4 days: staining spreads.
– Veins go "marbled" - a brownish black discoloration
• 5-6 days: abdomen swells with gas.
– Skin blisters
• 2 weeks: abdomen very tight and swollen.
• 3 weeks: tissue softens. Organs and cavities bursting. Nails fall off
• 4 weeks: soft tissues begin to liquefy. Face becoming unrecognizable
• 4 - 6 months: formation of adipocere, if in damp place.
– This is when the fat goes all hard and waxy.
• A body without a coffin will be decayed within 12 years.
Influences on Putrefaction
A high environmental humidity will enhance putrefaction.
The rate of putrefaction is influenced by the bodily habits of the decedent;
obese individuals putrefy more rapidly than those who are lean.
Putrefaction will be delayed in deaths from exsanguination (bleeding to death)
because blood provides a channel for the spread of putrefactive organisms
within the body.
Conversely, putrefaction is more rapid in persons dying with widespread
infection, congestive cardiac failure or retention of sodium and salts.
It tends to be more rapid in children than in adults, but the onset is relatively
slow in unfed new-born infants because of the lack of commensal bacteria.
• Heavy clothing and other
coverings, by retaining body
heat, will speed up
• Rapid putrefactive changes
may be seen in corpses left
in a room which is well
heated, or in a bed with an
• Injuries to the body surface
promote putrefaction by
providing portals of entry
for bacteria and the
associated blood provides an
excellent medium for
Electrical contractility of muscle
• During supravital period electrical contractility of
muscle can be used to calculate TSD up to 2-3 hrs.
Bone marrow cell change
• Bone marrow is aspirated from the sternum
• Deposited on glass slide, smear made and
stained by cytochemical stains like
1 hr- no appreciable change
1-2 hrs-occasional pyknotic erythroblasts are
seen,budding of nucleus.
-3hrs-pyknotic erythroblasts are more common.
-6hrs-early neutrophil lysis by vacuolation of the
9-12 hrs-advance neutrophils lysis.
12 hrs-all myelocyte lise.
Nasal ciliary motility
• Nasal cilia maintain motility up to 18 hrs after
Stomach Emptying as a measure of time since a
• Average meal last for 2-3 hrs.
• Vegitable meal- 4-6 hrs.
• Farinaceous meal- 6-7 hrs.
• Stomach empting starts within 10 min of swallowing.
• Light meal-1- 2 hrs.
• Medium meal- 3-4 hrs.
• Heavy meal- 5-6 hrs.
• Meal reaches to ileocaecal valve between 6 and 8 hrs.
• Movement of food distal to stomach-
• Hepatic flexure-6hrs
• Splenic flexure-9-12 hrs
• Pelvic colone -12-18 hrs
1. If undigested stomach contents are present, then death
occurred 0 to 2 hrs after last meal.
2. If stomach is empty but food is found in the small intestine,
then death occurred at least 4 to 6 hrs after a meal.
3. If the small intestine is empty and wastes are found in the
large intestine, the death occurred 12 or more hours after a
Glycolysis in the PM period occures at a rate of
Blood glucose levels are not useful PMI
indicator because of several variables like ,
DM,cause of death(increase glucose levels in
asphyxia,co poisoning ,increased ICP)
• During life-plasma and RBC levels -1mEq/L
• 1hr after death-20 mEq/L
• 12-24 hrs after death-50-75mEq/L
-Creatinine, NPN,and total soluble protein all increase
linearly with PMI.
Amino acid nitrogen:
-Up to 10 hrs after death-<14mg%
-48 hrs >=30mg%
-no further increase after that.
Enzymes: all increase after death.
Acid phosphatase -within 48 hrs levels increase 20
Alkaline phosphatase -increases with PMI
Normal ante mortem range-1.5-4BU.
10 hrs after death-5.3 BU
18 hrs after death-9BU
48hrs after death-30 BU
Amylase: After 2 days levels are 3-4 times that of
normal ante mortem levels.
-Na levels-falls at rate of 0.90mEq/l/hr
Cl levels-falls at rate of 0.97mEq/l/hr
-k levels-incresed to18mEq/L after 1 hr,due to its
release from cells.Thereafter continues to increased
Ca-levels are constant upto 10hrs. Thereafter
P-Both organic and inorganic P increase after
death.After 18 hrs inorganic P increases to 20mEq/L
Glucose-decreases rapidly after death
Lactic acid- increases sharply and regularly upto 10 hrs
,thereafter continues to increase but at lower rate.
Inositol- normal level during life1.7±0.45mg%
-increases regularly after death ,up to 72mg%
Inorganic sulphates-stable up to 3 days after death
Potassium-increases in proportion up to 70 hrs after death.
Variation between two eyes may be upto 10%.
Glucose- normal vitreous glucose level are approximately half
of the serum level.
With increasing PMI there is a consistent decrease in level.
Within 4-5 hrs levels are zero in non diabetics.
Lactic acid- normal-80-160mg%,
after 20 hrs increase to 210-260mg%
calcium,-normal levels are 54.0-95.5mg/l,post-mortem change
Chloride-normal levels are 114mmol/l,change are insignificnts
Potassium- most usefull indicator
-During life k con is low in vitreous humour(5.8mmol/l)but
much higher in peripheral tissues like retina.
-After death k from peripheral tissues starts diffusing in the
vitreous increasing its concentrtion.
TSD(in hrs)=7.14x(k ion con in mmol/l)_39.1 (Sturner’s
TSD(in hrs)=5.26x(k ion con in mmol/l)-30.9 (Madea’s
TSD(in hrs)=4.32x(k ion con in mmol/l)-18.35 (James
Hypoxanthine show linear rise up to 120 hrs.
Na- Decreases 0.9 mmol/l/hr
Pericardial fluid – Not useful
-Potassium increase at rate of 0.30mmol/hrs
-Sodium decrease at rate of 0.37mmol/hrs in first
85 hrs after death.
Synovial fluid- K+ > 2X in first 2 days.
-Myofibrillar protease increases linearly
-Creatinine phosphokinase decreases linerly
Entomoogy of the cadaver
• Within minutes of death, certain insects arrive to lay their eggs on the warm
body, attracted by the smell of the first stages of decomposition.
• The eggs will hatch and feed on the tissues.
• Blowflies are a common example.
• Flesh flies are another example.
• Blowflies are attracted to two gases of decomposition:
As the corpse progresses through the stages, other kinds of insects will arrive.
– Tiny wasps come to lay their eggs on maggots already present in the body
– Cheese skippers arrive once putrefaction is underway; they are attracted
by the seepage of body fluids.
– Mites and beetles feed on dry tissues and hair
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 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.
The Scene Of Death
Cell phone record- death must have occurred
between last call attended and first call
Milk bottles- number uncollected milk bottles at
door step indicate number of days person is
Newspapers- earlist newspaper uncollected at
door step gives the possible date of death.
Stopped wrist watch- in cases of drowning ,fall from height,
blunt trauma etc where weapon struck watch and stopped, it
may rarely give exact time of death.
Dates on uncollected mail.
Sales receipts and date slips of paper in deceased’s pockets.
Statement from neighbours –when they last saw the deceased.
State of food on the table- fully completed , half eaten etc.
State of dress –whether the person was in normal dress or
night dress .
Corpse lying on grass –look at grass underneath the corpse.
- The state of drying ,yellowness etc can indicate time of
Radio carbon dating
• Half life of C-14 is 5730 years.knowing the
ratio of c-14/c-12 in body can give time of
• Lesser c-14 means more time o death and vice
• Can only date bodies more than 100 years
old.so virtually useless for medico legal
Brain RNA: Brain RNA degrades in a linear fashion after
death,18s r RNA is more stable than beta-actin m RNA in
the post-mortem period. their ratio can be used to predict
Flow cytometry: DNA start degrading immediately after
death, number of cells with degraded DNA would
increases as PM interval increases.
Histologic changes in the skin:
• <6hrs-epidermis,dermis,hair follicles ,sweat, and
sebaceous glands appear normal for 6hrs after death.
• After this period degenerative changes began.
• 6-9 hrs-degeneration starts in the dermis.
• 18hrs-dermis begins to disintegrate.
• >18hrs-hair follicles ,sweat and sebaceous glands
start showing degeneration.
Melatonin: is secreted into the blood by the pineal
Its synthesis increases vastly in night time and
decreases in day time.it is not influenced by
environmental factors except light.
If the melatonin levels in post-mortem blood , urine
, serum are high, it can be said that the individual
died in night time if low, in day time.
• Strontium-90: strontium-90 is an artificial nuclear
fission product of the atmospheric atomic bomb testing
• It was spread through out the atmosphere in the
• Strontium-90 is an analogue to calcium and therefor
deposited in human bones.
• Its half life 28.1years.
• During life strontium-90 is continuously being inheld
but after death it degrade continuously.
• Residual strontium-90 in bones is determined,it
indicates TSD just like in radiocarbon dating